diff --git a/src/x11_time.c b/src/x11_time.c
index e2203941..4184d326 100644
--- a/src/x11_time.c
+++ b/src/x11_time.c
@@ -39,7 +39,7 @@
 
 static uint64_t getRawTime(void)
 {
-#if defined(_POSIX_TIMERS) && defined(_POSIX_MONOTONIC_CLOCK)
+#if defined(CLOCK_MONOTONIC)
     if (_glfwLibrary.X11.timer.monotonic)
     {
         struct timespec ts;
@@ -64,7 +64,7 @@ static uint64_t getRawTime(void)
 
 void _glfwInitTimer(void)
 {
-#if defined(_POSIX_TIMERS) && defined(_POSIX_MONOTONIC_CLOCK)
+#if defined(CLOCK_MONOTONIC)
     struct timespec ts;
 
     if (clock_gettime(CLOCK_MONOTONIC, &ts) == 0)