diff --git a/client/X11/xf_x11_utils.c b/client/X11/xf_x11_utils.c
index 6bb741728..d577856c4 100644
--- a/client/X11/xf_x11_utils.c
+++ b/client/X11/xf_x11_utils.c
@@ -19,6 +19,8 @@
  */
 
 // Do not include! X11 has conflicting defines #include "xf_utils.h"
+const char* request_code_2_str(int code);
+
 #include <X11/Xproto.h>
 
 const char* request_code_2_str(int code)