diff --git a/src/regex/regcustom.h b/src/regex/regcustom.h
index bd55210c37..804c4b32af 100644
--- a/src/regex/regcustom.h
+++ b/src/regex/regcustom.h
@@ -43,6 +43,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <ctype.h>
 #include <limits.h>