diff --git a/src/util/u_string.h b/src/util/u_string.h
index 5a2a3e9817f..fa0241e5423 100644
--- a/src/util/u_string.h
+++ b/src/util/u_string.h
@@ -41,6 +41,7 @@
 #include <stdlib.h>
 #include <stddef.h>
 #include <stdarg.h>
+#include <string.h>
 
 #include "util/macros.h" // PRINTFLIKE