diff --git a/tests/libtest/test.h b/tests/libtest/test.h
index a0d4308429..1e5b67c967 100644
--- a/tests/libtest/test.h
+++ b/tests/libtest/test.h
@@ -1,5 +1,6 @@
 #include <curl.h>
 #include <stdio.h>
+#include <string.h>
 
 extern char *arg2; /* set by first.c to the argv[2] or NULL */