diff --git a/include/polarssl/entropy.h b/include/polarssl/entropy.h
index 92aa5a5..53a1f0e 100644
--- a/include/polarssl/entropy.h
+++ b/include/polarssl/entropy.h
@@ -24,14 +24,14 @@
 #ifndef POLARSSL_ENTROPY_H
 #define POLARSSL_ENTROPY_H
 
-#include <string.h>
-
 #if !defined(POLARSSL_CONFIG_FILE)
 #include "config.h"
 #else
 #include POLARSSL_CONFIG_FILE
 #endif
 
+#include <stddef.h>
+
 #if defined(POLARSSL_SHA512_C) && !defined(POLARSSL_ENTROPY_FORCE_SHA256)
 #include "sha512.h"
 #define POLARSSL_ENTROPY_SHA512_ACCUMULATOR