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;
diff --git a/unix/vncconfig/vncExt.h b/unix/vncconfig/vncExt.h
index f1502c4..e41e2e5 100644
--- a/unix/vncconfig/vncExt.h
+++ b/unix/vncconfig/vncExt.h
@@ -54,7 +54,7 @@
 Bool XVncExtSetServerCutText(Display* dpy, const char* str, int len);
 Bool XVncExtGetClientCutText(Display* dpy, char** str, int* len);
 Bool XVncExtSelectInput(Display* dpy, Window w, int mask);
-Bool XVncExtConnect(Display* dpy, char* hostAndPort);
+Bool XVncExtConnect(Display* dpy, const char* hostAndPort);
 Bool XVncExtGetQueryConnect(Display* dpy, char** addr,
                             char** user, int* timeout, void** opaqueId);
 Bool XVncExtApproveConnect(Display* dpy, void* opaqueId, int approve);