diff --git a/randr/rrsdispatch.c b/randr/rrsdispatch.c
index 2bc7dc1f6..cfd7afa4a 100644
--- a/randr/rrsdispatch.c
+++ b/randr/rrsdispatch.c
@@ -519,6 +519,9 @@ SProcRRChangeProviderProperty(ClientPtr client)
     case 32:
         SwapRestL(stuff);
         break;
+    default:
+        client->errorValue = stuff->format;
+        return BadValue;
     }
     return ProcRandrVector[stuff->randrReqType] (client);
 }