diff --git a/md5.c b/md5.c
index c0d45ad0b79860f25435a33d5a6341fa74ee43fc..932f6ca16b9f4060c745c7d8e99ca74f992b932d 100644
--- a/md5.c
+++ b/md5.c
@@ -31,6 +31,7 @@
 #include "macros.h"
 
 #include <assert.h>
+#include <string.h>
 
 /* A block, treated as a sequence of 32-bit words. */
 #define MD5_DATA_LENGTH 16