diff --git a/src/xkb/XKBGetMap.c b/src/xkb/XKBGetMap.c
index ea77f2a3..5551298c 100644
--- a/src/xkb/XKBGetMap.c
+++ b/src/xkb/XKBGetMap.c
@@ -425,6 +425,9 @@ xkbVModMapWireDesc *	wire;
 XkbServerMapPtr		srv;
 
     if ( rep->totalVModMapKeys>0 ) {
+	if (((int) rep->firstVModMapKey + rep->nVModMapKeys)
+	     > xkb->max_key_code)
+	    return BadLength;
 	if (((xkb->server==NULL)||(xkb->server->vmodmap==NULL))&&
 	    (XkbAllocServerMap(xkb,XkbVirtualModMapMask,0)!=Success)) {
 	    return BadAlloc;