diff --git a/unix/vncconfig/vncExt.c b/unix/vncconfig/vncExt.c
index eef7c4b..ff6b4d6 100644
--- a/unix/vncconfig/vncExt.c
+++ b/unix/vncconfig/vncExt.c
@@ -278,7 +278,7 @@
   return True;
 }
 
-Bool XVncExtConnect(Display* dpy, char* hostAndPort)
+Bool XVncExtConnect(Display* dpy, const char* hostAndPort)
 {
   xVncExtConnectReq* req;
   xVncExtConnectReply rep;