diff --git a/crypto/ui/ui_compat.c b/crypto/ui/ui_compat.c
index 6938d72d49..701c07c181 100644
--- a/crypto/ui/ui_compat.c
+++ b/crypto/ui/ui_compat.c
@@ -57,6 +57,7 @@
  * [including the GNU Public Licence.]
  */
 
+#include <string.h>
 #include <openssl/ui_compat.h>
 
 #ifndef OPENSSL_NO_DES