diff --git a/library/entropy_poll.c b/library/entropy_poll.c
index 467268c..8d98d89 100644
--- a/library/entropy_poll.c
+++ b/library/entropy_poll.c
@@ -32,6 +32,7 @@
 #include "polarssl/entropy_poll.h"
 
 #if defined(POLARSSL_TIMING_C)
+#include <string.h>
 #include "polarssl/timing.h"
 #endif
 #if defined(POLARSSL_HAVEGE_C)