diff --git a/sigdwmblocks.c b/sigdwmblocks.c
index 7c07104..3709c14 100644
--- a/sigdwmblocks.c
+++ b/sigdwmblocks.c
@@ -10,8 +10,42 @@
 #define NILL                            INT_MIN
 #define LOCKFILE                        "/tmp/dwmblocks.pid"
 
+int
+parsesignal(char *c, int *s)
+{
+        for (*s = 0; *c != '\0'; c++)
+                if (*c >= '0' && *c <= '9') {
+                        *s *= 10;
+                        *s += *c - '0';
+                } else
+                        return 0;
+        if ((*s += SIGRTMIN) > SIGRTMAX)
+                return 0;
+        return 1;
+}
+
+int
+parsesigval(char *c, int *v)
+{
+        int s = 1;
+
+        if (*c == '-') {
+                s = -1;
+                c++;
+        } else if (*c == '+')
+                c++;
+        for (*v = 0; *c != '\0'; c++)
+                if (*c >= '0' && *c <= '9') {
+                        *v *= 10;
+                        *v += *c - '0';
+                } else
+                        return 0;
+        *v *= s;
+        return 1;
+}
+
 void
-sendsignal(int signum, union sigval sv)
+sendsignal(int sig, union sigval sv)
 {
         int fd;
         struct flock fl;
@@ -37,11 +71,8 @@ sendsignal(int signum, union sigval sv)
                 fputs("Error: no running instance of dwmblocks.\n", stderr);
                 exit(3);
         }
-        if (sigqueue(fl.l_pid, signum, sv) == -1) {
-                if (errno == EINVAL) {
-                        fputs("Error: invalid signal provided in argument.\n", stderr);
-                        exit(2);
-                } else if (errno == ESRCH) {
+        if (sigqueue(fl.l_pid, sig, sv) == -1) {
+                if (errno == ESRCH) {
                         fputs("Error: no running instance of dwmblocks.\n", stderr);
                         exit(3);
                 } else {
@@ -54,21 +85,17 @@ sendsignal(int signum, union sigval sv)
 int
 main(int argc, char *argv[])
 {
-        if (argc > 1) {
-                int signal;
-                union sigval sv;
+        int sig;
+        union sigval sv;
 
-                if (sscanf(argv[1], "%d", &signal) == 1 &&
-                    signal > 0 && (signal += SIGRTMIN) <= SIGRTMAX) {
-                        if (argc == 2) {
-                                sv.sival_int = NILL;
-                                sendsignal(signal, sv);
-                                return 0;
-                        } else if (argc == 3 &&
-                                   sscanf(argv[2], "%d", &(sv.sival_int)) == 1) {
-                                sendsignal(signal, sv);
-                                return 0;
-                        }
+        if (argc > 1 && parsesignal(argv[1], &sig)) {
+                if (argc == 2) {
+                        sv.sival_int = NILL;
+                        sendsignal(sig, sv);
+                        return 0;
+                } else if (argc == 3 && parsesigval(argv[2], &(sv.sival_int))) {
+                        sendsignal(sig, sv);
+                        return 0;
                 }
         }
         fprintf(stderr, "Usage: %s <signal> [<sigval>]\n", argv[0]);