diff --git a/common/rfb/SMsgWriter.cxx b/common/rfb/SMsgWriter.cxx
index cf3264e..bc3f439 100644
--- a/common/rfb/SMsgWriter.cxx
+++ b/common/rfb/SMsgWriter.cxx
@@ -101,7 +101,9 @@
   os->writeU32(flags);
 
   os->writeU8(len);
-  os->writeBytes(data, len);
+
+  if (len > 0)
+    os->writeBytes(data, len);
 
   endMsg();
 }