diff --git a/library/entropy.c b/library/entropy.c
index 7f95317..bc7fb0f 100644
--- a/library/entropy.c
+++ b/library/entropy.c
@@ -385,6 +385,7 @@
 #if defined(POLARSSL_PLATFORM_C)
 #include "polarssl/platform.h"
 #else
+#include <stdio.h>
 #define polarssl_printf     printf
 #endif