diff --git a/common/rfb/CMsgReader.cxx b/common/rfb/CMsgReader.cxx
index e3b73bf..63d31d1 100644
--- a/common/rfb/CMsgReader.cxx
+++ b/common/rfb/CMsgReader.cxx
@@ -100,7 +100,7 @@
     readCopyRect(r);
   } else {
 
-    if (encoding > encodingMax) {
+    if (!Decoder::supported(encoding)) {
       fprintf(stderr, "Unknown rect encoding %d\n", encoding);
       throw Exception("Unknown rect encoding");
     }