diff --git a/common/rfb/TightDecoder.cxx b/common/rfb/TightDecoder.cxx
index c547053..548c190 100644
--- a/common/rfb/TightDecoder.cxx
+++ b/common/rfb/TightDecoder.cxx
@@ -269,7 +269,7 @@
         size_t len = palSize * 3;
         rdr::U8Array tightPalette(len);
 
-        assert(buflen >= sizeof(len));
+        assert(buflen >= len);
 
         memcpy(tightPalette.buf, bufptr, len);
         bufptr += len;