diff --git a/src/rng.c b/src/rng.c
index 8f3a74a..46f50db 100644
--- a/src/rng.c
+++ b/src/rng.c
@@ -71,14 +71,16 @@ void rng_init(void) {
 static uint32_t rng_timeEntropy(void) {
   int i;
   
-#ifdef WIN32
+#if defined(_POSIX_SOURCE)
+  struct timeval tv;
+  gettimeofday(&tv, NULL);
+  i = tv.tv_sec * 1000000 + tv.tv_usec;
+#elif defined(WIN32)
   struct _timeb tb;
   _ftime(&tb);
   i = tb.time * 1000 + tb.millitm;
 #else
-  struct timeval tv;
-  gettimeofday(&tv, NULL);
-  i = tv.tv_sec * 1000000 + tv.tv_usec;
+#error "Needs Implmentation."
 #endif
   return i;
 }