diff --git a/platform-specific/dtls_prng_win.c b/platform-specific/dtls_prng_win.c
index 8bd96002..a71633b2 100644
--- a/platform-specific/dtls_prng_win.c
+++ b/platform-specific/dtls_prng_win.c
@@ -15,8 +15,6 @@
 #include "dtls_prng.h"
 #include "dtls_debug.h"
 
-#define _CRT_RAND_S
-
 #include <stdlib.h>
 
 #if defined(__MINGW32__)
diff --git a/tinydtls.h b/tinydtls.h
index 54ff9315..33b7d3cc 100644
--- a/tinydtls.h
+++ b/tinydtls.h
@@ -34,6 +34,7 @@
 
 #if defined(_WIN32) || defined(_WIN64)
 #define IS_WINDOWS 1
+#define _CRT_RAND_S
 #endif
 
 #ifdef WITH_LWIP