diff --git a/crypto/modes/gcm_test.c b/crypto/modes/gcm_test.c
index 5308976..29f9d95 100644
--- a/crypto/modes/gcm_test.c
+++ b/crypto/modes/gcm_test.c
@@ -47,6 +47,7 @@
  * ==================================================================== */
 
 #include <stdio.h>
+#include <string.h>
 
 #include <openssl/aes.h>
 #include <openssl/crypto.h>