diff --git a/dlls/ntdll/signal_arm.c b/dlls/ntdll/signal_arm.c
index 5ee9f453333..cb5f67db75b 100644
--- a/dlls/ntdll/signal_arm.c
+++ b/dlls/ntdll/signal_arm.c
@@ -860,7 +860,7 @@ static void usr1_handler( int signal, siginfo_t *siginfo, void *sigcontext )
  */
 int CDECL __wine_set_signal_handler(unsigned int sig, wine_signal_handler wsh)
 {
-    if (sig > sizeof(handlers) / sizeof(handlers[0])) return -1;
+    if (sig >= sizeof(handlers) / sizeof(handlers[0])) return -1;
     if (handlers[sig] != NULL) return -2;
     handlers[sig] = wsh;
     return 0;
diff --git a/dlls/ntdll/signal_arm64.c b/dlls/ntdll/signal_arm64.c
index 3a41c8405cc..14c5260c148 100644
--- a/dlls/ntdll/signal_arm64.c
+++ b/dlls/ntdll/signal_arm64.c
@@ -732,7 +732,7 @@ static void usr1_handler( int signal, siginfo_t *siginfo, void *sigcontext )
  */
 int CDECL __wine_set_signal_handler(unsigned int sig, wine_signal_handler wsh)
 {
-    if (sig > sizeof(handlers) / sizeof(handlers[0])) return -1;
+    if (sig >= sizeof(handlers) / sizeof(handlers[0])) return -1;
     if (handlers[sig] != NULL) return -2;
     handlers[sig] = wsh;
     return 0;
diff --git a/dlls/ntdll/signal_powerpc.c b/dlls/ntdll/signal_powerpc.c
index 886da863704..507490a5264 100644
--- a/dlls/ntdll/signal_powerpc.c
+++ b/dlls/ntdll/signal_powerpc.c
@@ -940,7 +940,7 @@ static void usr1_handler( int signal, siginfo_t *siginfo, void *sigcontext )
  */
 int CDECL __wine_set_signal_handler(unsigned int sig, wine_signal_handler wsh)
 {
-    if (sig > sizeof(handlers) / sizeof(handlers[0])) return -1;
+    if (sig >= sizeof(handlers) / sizeof(handlers[0])) return -1;
     if (handlers[sig] != NULL) return -2;
     handlers[sig] = wsh;
     return 0;
diff --git a/dlls/ntdll/signal_x86_64.c b/dlls/ntdll/signal_x86_64.c
index 1e88df31437..a79fd6eb47d 100644
--- a/dlls/ntdll/signal_x86_64.c
+++ b/dlls/ntdll/signal_x86_64.c
@@ -2762,7 +2762,7 @@ static void usr1_handler( int signal, siginfo_t *siginfo, void *ucontext )
  */
 int CDECL __wine_set_signal_handler(unsigned int sig, wine_signal_handler wsh)
 {
-    if (sig > sizeof(handlers) / sizeof(handlers[0])) return -1;
+    if (sig >= sizeof(handlers) / sizeof(handlers[0])) return -1;
     if (handlers[sig] != NULL) return -2;
     handlers[sig] = wsh;
     return 0;