diff --git a/internal/api/client/filters/v1/filterpost_test.go b/internal/api/client/filters/v1/filterpost_test.go
index 2b18abf13..b7aecc573 100644
--- a/internal/api/client/filters/v1/filterpost_test.go
+++ b/internal/api/client/filters/v1/filterpost_test.go
@@ -41,6 +41,7 @@ func (suite *FiltersTestSuite) postFilter(
 	irreversible *bool,
 	wholeWord *bool,
 	expiresIn *int,
+	expiresInStr *string,
 	requestJson *string,
 	expectedHTTPStatus int,
 	expectedBody string,
@@ -75,6 +76,8 @@ func (suite *FiltersTestSuite) postFilter(
 		}
 		if expiresIn != nil {
 			ctx.Request.Form["expires_in"] = []string{strconv.Itoa(*expiresIn)}
+		} else if expiresInStr != nil {
+			ctx.Request.Form["expires_in"] = []string{*expiresInStr}
 		}
 	}
 
@@ -124,7 +127,7 @@ func (suite *FiltersTestSuite) TestPostFilterFull() {
 	irreversible := false
 	wholeWord := true
 	expiresIn := 86400
-	filter, err := suite.postFilter(&phrase, &context, &irreversible, &wholeWord, &expiresIn, nil, http.StatusOK, "")
+	filter, err := suite.postFilter(&phrase, &context, &irreversible, &wholeWord, &expiresIn, nil, nil, http.StatusOK, "")
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -155,7 +158,7 @@ func (suite *FiltersTestSuite) TestPostFilterFullJSON() {
 		"whole_word": true,
 		"expires_in": 86400.1
 	}`
-	filter, err := suite.postFilter(nil, nil, nil, nil, nil, &requestJson, http.StatusOK, "")
+	filter, err := suite.postFilter(nil, nil, nil, nil, nil, nil, &requestJson, http.StatusOK, "")
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -182,7 +185,7 @@ func (suite *FiltersTestSuite) TestPostFilterMinimal() {
 
 	phrase := "GNU/Linux"
 	context := []string{"home"}
-	filter, err := suite.postFilter(&phrase, &context, nil, nil, nil, nil, http.StatusOK, "")
+	filter, err := suite.postFilter(&phrase, &context, nil, nil, nil, nil, nil, http.StatusOK, "")
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -203,7 +206,7 @@ func (suite *FiltersTestSuite) TestPostFilterMinimal() {
 func (suite *FiltersTestSuite) TestPostFilterEmptyPhrase() {
 	phrase := ""
 	context := []string{"home"}
-	_, err := suite.postFilter(&phrase, &context, nil, nil, nil, nil, http.StatusUnprocessableEntity, "")
+	_, err := suite.postFilter(&phrase, &context, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, "")
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -211,7 +214,7 @@ func (suite *FiltersTestSuite) TestPostFilterEmptyPhrase() {
 
 func (suite *FiltersTestSuite) TestPostFilterMissingPhrase() {
 	context := []string{"home"}
-	_, err := suite.postFilter(nil, &context, nil, nil, nil, nil, http.StatusUnprocessableEntity, "")
+	_, err := suite.postFilter(nil, &context, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, "")
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -220,7 +223,7 @@ func (suite *FiltersTestSuite) TestPostFilterMissingPhrase() {
 func (suite *FiltersTestSuite) TestPostFilterEmptyContext() {
 	phrase := "GNU/Linux"
 	context := []string{}
-	_, err := suite.postFilter(&phrase, &context, nil, nil, nil, nil, http.StatusUnprocessableEntity, "")
+	_, err := suite.postFilter(&phrase, &context, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, "")
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -228,7 +231,7 @@ func (suite *FiltersTestSuite) TestPostFilterEmptyContext() {
 
 func (suite *FiltersTestSuite) TestPostFilterMissingContext() {
 	phrase := "GNU/Linux"
-	_, err := suite.postFilter(&phrase, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, "")
+	_, err := suite.postFilter(&phrase, nil, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, "")
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -237,8 +240,37 @@ func (suite *FiltersTestSuite) TestPostFilterMissingContext() {
 // There should be a filter with this phrase as its title in our test fixtures. Creating another should fail.
 func (suite *FiltersTestSuite) TestPostFilterTitleConflict() {
 	phrase := "fnord"
-	_, err := suite.postFilter(&phrase, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, "")
+	_, err := suite.postFilter(&phrase, nil, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, "")
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
 }
+
+// postFilterWithExpiration creates a filter with optional expiration.
+func (suite *FiltersTestSuite) postFilterWithExpiration(phrase *string, expiresIn *int, expiresInStr *string, requestJson *string) *apimodel.FilterV1 {
+	context := []string{"home"}
+	filter, err := suite.postFilter(phrase, &context, nil, nil, expiresIn, expiresInStr, requestJson, http.StatusOK, "")
+	if err != nil {
+		suite.FailNow(err.Error())
+	}
+	return filter
+}
+
+// Regression test for https://github.com/superseriousbusiness/gotosocial/issues/3497
+func (suite *FiltersTestSuite) TestPostFilterWithEmptyStringExpiration() {
+	title := "Form Sins"
+	expiresInStr := ""
+	filter := suite.postFilterWithExpiration(&title, nil, &expiresInStr, nil)
+	suite.Nil(filter.ExpiresAt)
+}
+
+// Regression test related to https://github.com/superseriousbusiness/gotosocial/issues/3497
+func (suite *FiltersTestSuite) TestPostFilterWithNullExpirationJSON() {
+	requestJson := `{
+		"phrase": "JSON Sins",
+		"context": ["home"],
+		"expires_in": null
+	}`
+	filter := suite.postFilterWithExpiration(nil, nil, nil, &requestJson)
+	suite.Nil(filter.ExpiresAt)
+}
diff --git a/internal/api/client/filters/v1/filterput_test.go b/internal/api/client/filters/v1/filterput_test.go
index 40b52ee43..626bd52eb 100644
--- a/internal/api/client/filters/v1/filterput_test.go
+++ b/internal/api/client/filters/v1/filterput_test.go
@@ -42,6 +42,7 @@ func (suite *FiltersTestSuite) putFilter(
 	irreversible *bool,
 	wholeWord *bool,
 	expiresIn *int,
+	expiresInStr *string,
 	requestJson *string,
 	expectedHTTPStatus int,
 	expectedBody string,
@@ -76,6 +77,8 @@ func (suite *FiltersTestSuite) putFilter(
 		}
 		if expiresIn != nil {
 			ctx.Request.Form["expires_in"] = []string{strconv.Itoa(*expiresIn)}
+		} else if expiresInStr != nil {
+			ctx.Request.Form["expires_in"] = []string{*expiresInStr}
 		}
 	}
 
@@ -128,7 +131,7 @@ func (suite *FiltersTestSuite) TestPutFilterFull() {
 	irreversible := false
 	wholeWord := true
 	expiresIn := 86400
-	filter, err := suite.putFilter(id, &phrase, &context, &irreversible, &wholeWord, &expiresIn, nil, http.StatusOK, "")
+	filter, err := suite.putFilter(id, &phrase, &context, &irreversible, &wholeWord, &expiresIn, nil, nil, http.StatusOK, "")
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -160,7 +163,7 @@ func (suite *FiltersTestSuite) TestPutFilterFullJSON() {
 		"whole_word": true,
 		"expires_in": 86400.1
 	}`
-	filter, err := suite.putFilter(id, nil, nil, nil, nil, nil, &requestJson, http.StatusOK, "")
+	filter, err := suite.putFilter(id, nil, nil, nil, nil, nil, nil, &requestJson, http.StatusOK, "")
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -188,7 +191,7 @@ func (suite *FiltersTestSuite) TestPutFilterMinimal() {
 	id := suite.testFilterKeywords["local_account_1_filter_1_keyword_1"].ID
 	phrase := "GNU/Linux"
 	context := []string{"home"}
-	filter, err := suite.putFilter(id, &phrase, &context, nil, nil, nil, nil, http.StatusOK, "")
+	filter, err := suite.putFilter(id, &phrase, &context, nil, nil, nil, nil, nil, http.StatusOK, "")
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -210,7 +213,7 @@ func (suite *FiltersTestSuite) TestPutFilterEmptyPhrase() {
 	id := suite.testFilterKeywords["local_account_1_filter_1_keyword_1"].ID
 	phrase := ""
 	context := []string{"home"}
-	_, err := suite.putFilter(id, &phrase, &context, nil, nil, nil, nil, http.StatusUnprocessableEntity, "")
+	_, err := suite.putFilter(id, &phrase, &context, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, "")
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -219,7 +222,7 @@ func (suite *FiltersTestSuite) TestPutFilterEmptyPhrase() {
 func (suite *FiltersTestSuite) TestPutFilterMissingPhrase() {
 	id := suite.testFilterKeywords["local_account_1_filter_1_keyword_1"].ID
 	context := []string{"home"}
-	_, err := suite.putFilter(id, nil, &context, nil, nil, nil, nil, http.StatusUnprocessableEntity, "")
+	_, err := suite.putFilter(id, nil, &context, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, "")
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -229,7 +232,7 @@ func (suite *FiltersTestSuite) TestPutFilterEmptyContext() {
 	id := suite.testFilterKeywords["local_account_1_filter_1_keyword_1"].ID
 	phrase := "GNU/Linux"
 	context := []string{}
-	_, err := suite.putFilter(id, &phrase, &context, nil, nil, nil, nil, http.StatusUnprocessableEntity, "")
+	_, err := suite.putFilter(id, &phrase, &context, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, "")
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -238,7 +241,7 @@ func (suite *FiltersTestSuite) TestPutFilterEmptyContext() {
 func (suite *FiltersTestSuite) TestPutFilterMissingContext() {
 	id := suite.testFilterKeywords["local_account_1_filter_1_keyword_1"].ID
 	phrase := "GNU/Linux"
-	_, err := suite.putFilter(id, &phrase, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, "")
+	_, err := suite.putFilter(id, &phrase, nil, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, "")
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -248,7 +251,7 @@ func (suite *FiltersTestSuite) TestPutFilterMissingContext() {
 func (suite *FiltersTestSuite) TestPutFilterTitleConflict() {
 	id := suite.testFilterKeywords["local_account_1_filter_1_keyword_1"].ID
 	phrase := "metasyntactic variables"
-	_, err := suite.putFilter(id, &phrase, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, "")
+	_, err := suite.putFilter(id, &phrase, nil, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, "")
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -258,7 +261,7 @@ func (suite *FiltersTestSuite) TestPutAnotherAccountsFilter() {
 	id := suite.testFilterKeywords["local_account_2_filter_1_keyword_1"].ID
 	phrase := "GNU/Linux"
 	context := []string{"home"}
-	_, err := suite.putFilter(id, &phrase, &context, nil, nil, nil, nil, http.StatusNotFound, `{"error":"Not Found"}`)
+	_, err := suite.putFilter(id, &phrase, &context, nil, nil, nil, nil, nil, http.StatusNotFound, `{"error":"Not Found"}`)
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -268,8 +271,60 @@ func (suite *FiltersTestSuite) TestPutNonexistentFilter() {
 	id := "not_even_a_real_ULID"
 	phrase := "GNU/Linux"
 	context := []string{"home"}
-	_, err := suite.putFilter(id, &phrase, &context, nil, nil, nil, nil, http.StatusNotFound, `{"error":"Not Found"}`)
+	_, err := suite.putFilter(id, &phrase, &context, nil, nil, nil, nil, nil, http.StatusNotFound, `{"error":"Not Found"}`)
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
 }
+
+// setFilterExpiration sets filter expiration.
+func (suite *FiltersTestSuite) setFilterExpiration(id string, phrase *string, expiresIn *int, expiresInStr *string, requestJson *string) *apimodel.FilterV1 {
+	context := []string{"home"}
+	filter, err := suite.putFilter(id, phrase, &context, nil, nil, expiresIn, expiresInStr, requestJson, http.StatusOK, "")
+	if err != nil {
+		suite.FailNow(err.Error())
+	}
+	return filter
+}
+
+// Regression test for https://github.com/superseriousbusiness/gotosocial/issues/3497
+func (suite *FiltersTestSuite) TestPutFilterUnsetExpirationDateEmptyString() {
+	filterKeyword := suite.testFilterKeywords["local_account_1_filter_1_keyword_1"]
+	id := filterKeyword.ID
+	phrase := filterKeyword.Keyword
+
+	// Setup: set an expiration date for the filter.
+	expiresIn := 86400
+	filter := suite.setFilterExpiration(id, &phrase, &expiresIn, nil, nil)
+	if !suite.NotNil(filter.ExpiresAt) {
+		suite.FailNow("Test precondition failed")
+	}
+
+	// Unset the filter's expiration date by setting it to an empty string.
+	expiresInStr := ""
+	filter = suite.setFilterExpiration(id, &phrase, nil, &expiresInStr, nil)
+	suite.Nil(filter.ExpiresAt)
+}
+
+// Regression test related to https://github.com/superseriousbusiness/gotosocial/issues/3497
+func (suite *FiltersTestSuite) TestPutFilterUnsetExpirationDateNullJSON() {
+	filterKeyword := suite.testFilterKeywords["local_account_1_filter_1_keyword_1"]
+	id := filterKeyword.ID
+	phrase := filterKeyword.Keyword
+
+	// Setup: set an expiration date for the filter.
+	expiresIn := 86400
+	filter := suite.setFilterExpiration(id, &phrase, &expiresIn, nil, nil)
+	if !suite.NotNil(filter.ExpiresAt) {
+		suite.FailNow("Test precondition failed")
+	}
+
+	// Unset the filter's expiration date by setting it to a null literal.
+	requestJson := `{
+		"phrase": "fnord",
+		"context": ["home"],
+		"expires_in": null
+	}`
+	filter = suite.setFilterExpiration(id, nil, nil, nil, &requestJson)
+	suite.Nil(filter.ExpiresAt)
+}
diff --git a/internal/api/client/filters/v2/filterpost_test.go b/internal/api/client/filters/v2/filterpost_test.go
index 6e378874c..7a79f4665 100644
--- a/internal/api/client/filters/v2/filterpost_test.go
+++ b/internal/api/client/filters/v2/filterpost_test.go
@@ -36,7 +36,7 @@
 	"github.com/superseriousbusiness/gotosocial/testrig"
 )
 
-func (suite *FiltersTestSuite) postFilter(title *string, context *[]string, action *string, expiresIn *int, keywordsAttributesKeyword *[]string, keywordsAttributesWholeWord *[]bool, statusesAttributesStatusID *[]string, requestJson *string, expectedHTTPStatus int, expectedBody string) (*apimodel.FilterV2, error) {
+func (suite *FiltersTestSuite) postFilter(title *string, context *[]string, action *string, expiresIn *int, expiresInStr *string, keywordsAttributesWholeWord *[]bool, statusesAttributesStatusID *[]string, requestJson *string, expectedHTTPStatus int, expectedBody string, keywordsAttributesKeyword *[]string) (*apimodel.FilterV2, error) {
 	// instantiate recorder + test context
 	recorder := httptest.NewRecorder()
 	ctx, _ := testrig.CreateGinTestContext(recorder, nil)
@@ -64,6 +64,8 @@ func (suite *FiltersTestSuite) postFilter(title *string, context *[]string, acti
 		}
 		if expiresIn != nil {
 			ctx.Request.Form["expires_in"] = []string{strconv.Itoa(*expiresIn)}
+		} else if expiresInStr != nil {
+			ctx.Request.Form["expires_in"] = []string{*expiresInStr}
 		}
 		if keywordsAttributesKeyword != nil {
 			ctx.Request.Form["keywords_attributes[][keyword]"] = *keywordsAttributesKeyword
@@ -130,7 +132,7 @@ func (suite *FiltersTestSuite) TestPostFilterFull() {
 	keywordsAttributesWholeWord := []bool{true, false}
 	// Checked in lexical order by status ID, so keep this sorted.
 	statusAttributesStatusID := []string{"01HEN2QRFA8H3C6QPN7RD4KSR6", "01HEWV37MHV8BAC8ANFGVRRM5D"}
-	filter, err := suite.postFilter(&title, &context, &action, &expiresIn, &keywordsAttributesKeyword, &keywordsAttributesWholeWord, &statusAttributesStatusID, nil, http.StatusOK, "")
+	filter, err := suite.postFilter(&title, &context, &action, &expiresIn, nil, &keywordsAttributesWholeWord, &statusAttributesStatusID, nil, http.StatusOK, "", &keywordsAttributesKeyword)
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -197,7 +199,7 @@ func (suite *FiltersTestSuite) TestPostFilterFullJSON() {
 			}
 		]
 	}`
-	filter, err := suite.postFilter(nil, nil, nil, nil, nil, nil, nil, &requestJson, http.StatusOK, "")
+	filter, err := suite.postFilter(nil, nil, nil, nil, nil, nil, nil, &requestJson, http.StatusOK, "", nil)
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -245,7 +247,7 @@ func (suite *FiltersTestSuite) TestPostFilterMinimal() {
 
 	title := "GNU/Linux"
 	context := []string{"home"}
-	filter, err := suite.postFilter(&title, &context, nil, nil, nil, nil, nil, nil, http.StatusOK, "")
+	filter, err := suite.postFilter(&title, &context, nil, nil, nil, nil, nil, nil, http.StatusOK, "", nil)
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -267,7 +269,7 @@ func (suite *FiltersTestSuite) TestPostFilterMinimal() {
 func (suite *FiltersTestSuite) TestPostFilterEmptyTitle() {
 	title := ""
 	context := []string{"home"}
-	_, err := suite.postFilter(&title, &context, nil, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, "")
+	_, err := suite.postFilter(&title, &context, nil, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, "", nil)
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -275,7 +277,7 @@ func (suite *FiltersTestSuite) TestPostFilterEmptyTitle() {
 
 func (suite *FiltersTestSuite) TestPostFilterMissingTitle() {
 	context := []string{"home"}
-	_, err := suite.postFilter(nil, &context, nil, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, "")
+	_, err := suite.postFilter(nil, &context, nil, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, "", nil)
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -284,7 +286,7 @@ func (suite *FiltersTestSuite) TestPostFilterMissingTitle() {
 func (suite *FiltersTestSuite) TestPostFilterEmptyContext() {
 	title := "GNU/Linux"
 	context := []string{}
-	_, err := suite.postFilter(&title, &context, nil, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, "")
+	_, err := suite.postFilter(&title, &context, nil, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, "", nil)
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -292,7 +294,7 @@ func (suite *FiltersTestSuite) TestPostFilterEmptyContext() {
 
 func (suite *FiltersTestSuite) TestPostFilterMissingContext() {
 	title := "GNU/Linux"
-	_, err := suite.postFilter(&title, nil, nil, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, "")
+	_, err := suite.postFilter(&title, nil, nil, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, "", nil)
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -301,8 +303,37 @@ func (suite *FiltersTestSuite) TestPostFilterMissingContext() {
 // Creating another filter with the same title should fail.
 func (suite *FiltersTestSuite) TestPostFilterTitleConflict() {
 	title := suite.testFilters["local_account_1_filter_1"].Title
-	_, err := suite.postFilter(&title, nil, nil, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, "")
+	_, err := suite.postFilter(&title, nil, nil, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, "", nil)
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
 }
+
+// postFilterWithExpiration creates a filter with optional expiration.
+func (suite *FiltersTestSuite) postFilterWithExpiration(title *string, expiresIn *int, expiresInStr *string, requestJson *string) *apimodel.FilterV2 {
+	context := []string{"home"}
+	filter, err := suite.postFilter(title, &context, nil, expiresIn, expiresInStr, nil, nil, requestJson, http.StatusOK, "", nil)
+	if err != nil {
+		suite.FailNow(err.Error())
+	}
+	return filter
+}
+
+// Regression test for https://github.com/superseriousbusiness/gotosocial/issues/3497
+func (suite *FiltersTestSuite) TestPostFilterWithEmptyStringExpiration() {
+	title := "Form Crimes"
+	expiresInStr := ""
+	filter := suite.postFilterWithExpiration(&title, nil, &expiresInStr, nil)
+	suite.Nil(filter.ExpiresAt)
+}
+
+// Regression test related to https://github.com/superseriousbusiness/gotosocial/issues/3497
+func (suite *FiltersTestSuite) TestPostFilterWithNullExpirationJSON() {
+	requestJson := `{
+		"title": "JSON Crimes",
+		"context": ["home"],
+		"expires_in": null
+	}`
+	filter := suite.postFilterWithExpiration(nil, nil, nil, &requestJson)
+	suite.Nil(filter.ExpiresAt)
+}
diff --git a/internal/api/client/filters/v2/filterput.go b/internal/api/client/filters/v2/filterput.go
index cde03360d..2b440d5ca 100644
--- a/internal/api/client/filters/v2/filterput.go
+++ b/internal/api/client/filters/v2/filterput.go
@@ -18,7 +18,10 @@
 package v2
 
 import (
+	"bytes"
+	"encoding/json"
 	"errors"
+	"io"
 	"net/http"
 
 	"github.com/gin-gonic/gin"
@@ -180,12 +183,43 @@ func (m *Module) FilterPUTHandler(c *gin.Context) {
 		return
 	}
 
+	// If the request is JSON:
+	// Explicitly check whether `expires_in` is a null literal (vs. not being set at all).
+	hasNullExpiresIn := false
+	if c.ContentType() == gin.MIMEJSON {
+		// To do this, we need to read the request body twice, once here and once below for the form, so we buffer it.
+		// If a filter update request is bigger than a megabyte, somebody's messing with us.
+		bodyBytes, err := io.ReadAll(io.LimitReader(c.Request.Body, 1024*1024))
+		if err != nil {
+			apiutil.ErrorHandler(c, gtserror.NewErrorBadRequest(err, err.Error()), m.processor.InstanceGetV1)
+			return
+		}
+		c.Request.Body = io.NopCloser(bytes.NewReader(bodyBytes))
+
+		// Partially parse the body as a JSON object.
+		requestJSONObject := map[string]json.RawMessage{}
+		if err := json.Unmarshal(bodyBytes, &requestJSONObject); err != nil {
+			apiutil.ErrorHandler(c, gtserror.NewErrorBadRequest(err, err.Error()), m.processor.InstanceGetV1)
+			return
+		}
+
+		// Try to parse the `expires_in` field as a literal null.
+		if raw, found := requestJSONObject["expires_in"]; found {
+			hasNullExpiresIn = string(raw) == "null"
+		}
+	}
+
 	form := &apimodel.FilterUpdateRequestV2{}
 	if err := c.ShouldBind(form); err != nil {
 		apiutil.ErrorHandler(c, gtserror.NewErrorBadRequest(err, err.Error()), m.processor.InstanceGetV1)
 		return
 	}
 
+	// Interpret a literal null `expires_in` as unsetting the expiration date.
+	if hasNullExpiresIn {
+		form.ExpiresIn = util.Ptr(0)
+	}
+
 	if err := validateNormalizeUpdateFilter(form); err != nil {
 		apiutil.ErrorHandler(c, gtserror.NewErrorUnprocessableEntity(err, err.Error()), m.processor.InstanceGetV1)
 		return
@@ -283,11 +317,6 @@ func validateNormalizeUpdateFilter(form *apimodel.FilterUpdateRequestV2) error {
 		}
 	}
 
-	// Interpret zero as indefinite duration.
-	if form.ExpiresIn != nil && *form.ExpiresIn == 0 {
-		form.ExpiresIn = nil
-	}
-
 	// Normalize and validate updates.
 	for i, formKeyword := range form.Keywords {
 		if formKeyword.Keyword != nil {
diff --git a/internal/api/client/filters/v2/filterput_test.go b/internal/api/client/filters/v2/filterput_test.go
index d82d84b20..afa858ba9 100644
--- a/internal/api/client/filters/v2/filterput_test.go
+++ b/internal/api/client/filters/v2/filterput_test.go
@@ -36,7 +36,7 @@
 	"github.com/superseriousbusiness/gotosocial/testrig"
 )
 
-func (suite *FiltersTestSuite) putFilter(filterID string, title *string, context *[]string, action *string, expiresIn *int, keywordsAttributesID *[]string, keywordsAttributesKeyword *[]string, keywordsAttributesWholeWord *[]bool, keywordsAttributesDestroy *[]bool, statusesAttributesID *[]string, statusesAttributesStatusID *[]string, statusesAttributesDestroy *[]bool, requestJson *string, expectedHTTPStatus int, expectedBody string) (*apimodel.FilterV2, error) {
+func (suite *FiltersTestSuite) putFilter(filterID string, title *string, context *[]string, action *string, expiresIn *int, expiresInStr *string, keywordsAttributesKeyword *[]string, keywordsAttributesWholeWord *[]bool, keywordsAttributesDestroy *[]bool, statusesAttributesID *[]string, statusesAttributesStatusID *[]string, statusesAttributesDestroy *[]bool, requestJson *string, expectedHTTPStatus int, expectedBody string, keywordsAttributesID *[]string) (*apimodel.FilterV2, error) {
 	// instantiate recorder + test context
 	recorder := httptest.NewRecorder()
 	ctx, _ := testrig.CreateGinTestContext(recorder, nil)
@@ -64,6 +64,8 @@ func (suite *FiltersTestSuite) putFilter(filterID string, title *string, context
 		}
 		if expiresIn != nil {
 			ctx.Request.Form["expires_in"] = []string{strconv.Itoa(*expiresIn)}
+		} else if expiresInStr != nil {
+			ctx.Request.Form["expires_in"] = []string{*expiresInStr}
 		}
 		if keywordsAttributesID != nil {
 			ctx.Request.Form["keywords_attributes[][id]"] = *keywordsAttributesID
@@ -159,7 +161,7 @@ func (suite *FiltersTestSuite) TestPutFilterFull() {
 	keywordsAttributesWholeWord := []bool{true, false, true}
 	keywordsAttributesDestroy := []bool{false, true}
 	statusesAttributesStatusID := []string{suite.testStatuses["remote_account_1_status_2"].ID}
-	filter, err := suite.putFilter(id, &title, &context, &action, &expiresIn, &keywordsAttributesID, &keywordsAttributesKeyword, &keywordsAttributesWholeWord, &keywordsAttributesDestroy, nil, &statusesAttributesStatusID, nil, nil, http.StatusOK, "")
+	filter, err := suite.putFilter(id, &title, &context, &action, &expiresIn, nil, &keywordsAttributesKeyword, &keywordsAttributesWholeWord, &keywordsAttributesDestroy, nil, &statusesAttributesStatusID, nil, nil, http.StatusOK, "", &keywordsAttributesID)
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -231,7 +233,7 @@ func (suite *FiltersTestSuite) TestPutFilterFullJSON() {
 			}
 		]
 	}`
-	filter, err := suite.putFilter(id, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, &requestJson, http.StatusOK, "")
+	filter, err := suite.putFilter(id, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, &requestJson, http.StatusOK, "", nil)
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -281,7 +283,7 @@ func (suite *FiltersTestSuite) TestPutFilterMinimal() {
 	id := suite.testFilters["local_account_1_filter_1"].ID
 	title := "GNU/Linux"
 	context := []string{"home"}
-	filter, err := suite.putFilter(id, &title, &context, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, http.StatusOK, "")
+	filter, err := suite.putFilter(id, &title, &context, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, http.StatusOK, "", nil)
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -302,7 +304,7 @@ func (suite *FiltersTestSuite) TestPutFilterEmptyTitle() {
 	id := suite.testFilters["local_account_1_filter_1"].ID
 	title := ""
 	context := []string{"home"}
-	_, err := suite.putFilter(id, &title, &context, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, `{"error":"Unprocessable Entity: filter title must be provided, and must be no more than 200 chars"}`)
+	_, err := suite.putFilter(id, &title, &context, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, `{"error":"Unprocessable Entity: filter title must be provided, and must be no more than 200 chars"}`, nil)
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -312,7 +314,7 @@ func (suite *FiltersTestSuite) TestPutFilterEmptyContext() {
 	id := suite.testFilters["local_account_1_filter_1"].ID
 	title := "GNU/Linux"
 	context := []string{}
-	_, err := suite.putFilter(id, &title, &context, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, `{"error":"Unprocessable Entity: at least one filter context is required"}`)
+	_, err := suite.putFilter(id, &title, &context, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, http.StatusUnprocessableEntity, `{"error":"Unprocessable Entity: at least one filter context is required"}`, nil)
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -322,7 +324,7 @@ func (suite *FiltersTestSuite) TestPutFilterEmptyContext() {
 func (suite *FiltersTestSuite) TestPutFilterTitleConflict() {
 	id := suite.testFilters["local_account_1_filter_1"].ID
 	title := suite.testFilters["local_account_1_filter_2"].Title
-	_, err := suite.putFilter(id, &title, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, http.StatusConflict, `{"error":"Conflict: you already have a filter with this title"}`)
+	_, err := suite.putFilter(id, &title, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, http.StatusConflict, `{"error":"Conflict: you already have a filter with this title"}`, nil)
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -332,7 +334,7 @@ func (suite *FiltersTestSuite) TestPutAnotherAccountsFilter() {
 	id := suite.testFilters["local_account_2_filter_1"].ID
 	title := "GNU/Linux"
 	context := []string{"home"}
-	_, err := suite.putFilter(id, &title, &context, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, http.StatusNotFound, `{"error":"Not Found"}`)
+	_, err := suite.putFilter(id, &title, &context, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, http.StatusNotFound, `{"error":"Not Found"}`, nil)
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
@@ -342,8 +344,70 @@ func (suite *FiltersTestSuite) TestPutNonexistentFilter() {
 	id := "not_even_a_real_ULID"
 	phrase := "GNU/Linux"
 	context := []string{"home"}
-	_, err := suite.putFilter(id, &phrase, &context, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, http.StatusNotFound, `{"error":"Not Found"}`)
+	_, err := suite.putFilter(id, &phrase, &context, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, http.StatusNotFound, `{"error":"Not Found"}`, nil)
 	if err != nil {
 		suite.FailNow(err.Error())
 	}
 }
+
+// setFilterExpiration sets filter expiration.
+func (suite *FiltersTestSuite) setFilterExpiration(id string, expiresIn *int, expiresInStr *string, requestJson *string) *apimodel.FilterV2 {
+	filter, err := suite.putFilter(id, nil, nil, nil, expiresIn, expiresInStr, nil, nil, nil, nil, nil, nil, requestJson, http.StatusOK, "", nil)
+	if err != nil {
+		suite.FailNow(err.Error())
+	}
+	return filter
+}
+
+// Regression test for https://github.com/superseriousbusiness/gotosocial/issues/3497
+func (suite *FiltersTestSuite) TestPutFilterUnsetExpirationDateEmptyString() {
+	id := suite.testFilters["local_account_1_filter_2"].ID
+
+	// Setup: set an expiration date for the filter.
+	expiresIn := 86400
+	filter := suite.setFilterExpiration(id, &expiresIn, nil, nil)
+	if !suite.NotNil(filter.ExpiresAt) {
+		suite.FailNow("Test precondition failed")
+	}
+
+	// Unset the filter's expiration date by setting it to an empty string.
+	expiresInStr := ""
+	filter = suite.setFilterExpiration(id, nil, &expiresInStr, nil)
+	suite.Nil(filter.ExpiresAt)
+}
+
+// Regression test related to https://github.com/superseriousbusiness/gotosocial/issues/3497
+func (suite *FiltersTestSuite) TestPutFilterUnsetExpirationDateNullJSON() {
+	id := suite.testFilters["local_account_1_filter_3"].ID
+
+	// Setup: set an expiration date for the filter.
+	expiresIn := 86400
+	filter := suite.setFilterExpiration(id, &expiresIn, nil, nil)
+	if !suite.NotNil(filter.ExpiresAt) {
+		suite.FailNow("Test precondition failed")
+	}
+
+	// Unset the filter's expiration date by setting it to a null literal.
+	requestJson := `{
+		"expires_in": null
+	}`
+	filter = suite.setFilterExpiration(id, nil, nil, &requestJson)
+	suite.Nil(filter.ExpiresAt)
+}
+
+// Regression test related to https://github.com/superseriousbusiness/gotosocial/issues/3497
+func (suite *FiltersTestSuite) TestPutFilterUnalteredExpirationDateJSON() {
+	id := suite.testFilters["local_account_1_filter_4"].ID
+
+	// Setup: set an expiration date for the filter.
+	expiresIn := 86400
+	filter := suite.setFilterExpiration(id, &expiresIn, nil, nil)
+	if !suite.NotNil(filter.ExpiresAt) {
+		suite.FailNow("Test precondition failed")
+	}
+
+	// Update nothing. There should still be an expiration date.
+	requestJson := `{}`
+	filter = suite.setFilterExpiration(id, nil, nil, &requestJson)
+	suite.NotNil(filter.ExpiresAt)
+}
diff --git a/internal/processing/filters/v2/update.go b/internal/processing/filters/v2/update.go
index 0d443d58e..d5b5cce01 100644
--- a/internal/processing/filters/v2/update.go
+++ b/internal/processing/filters/v2/update.go
@@ -21,8 +21,6 @@
 	"context"
 	"errors"
 	"fmt"
-	"time"
-
 	apimodel "github.com/superseriousbusiness/gotosocial/internal/api/model"
 	"github.com/superseriousbusiness/gotosocial/internal/db"
 	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
@@ -30,6 +28,7 @@
 	"github.com/superseriousbusiness/gotosocial/internal/id"
 	"github.com/superseriousbusiness/gotosocial/internal/typeutils"
 	"github.com/superseriousbusiness/gotosocial/internal/util"
+	"time"
 )
 
 // Update an existing filter for the given account, using the provided parameters.
@@ -68,10 +67,16 @@ func (p *Processor) Update(
 		filterColumns = append(filterColumns, "action")
 		filter.Action = typeutils.APIFilterActionToFilterAction(*form.FilterAction)
 	}
-	// TODO: (Vyr) is it possible to unset a filter expiration with this API?
 	if form.ExpiresIn != nil {
+		expiresIn := *form.ExpiresIn
 		filterColumns = append(filterColumns, "expires_at")
-		filter.ExpiresAt = time.Now().Add(time.Second * time.Duration(*form.ExpiresIn))
+		if expiresIn == 0 {
+			// Unset the expiration date.
+			filter.ExpiresAt = time.Time{}
+		} else {
+			// Update the expiration date.
+			filter.ExpiresAt = time.Now().Add(time.Second * time.Duration(expiresIn))
+		}
 	}
 	if form.Context != nil {
 		filterColumns = append(filterColumns,