diff --git a/common/rfb/VNCServerST.cxx b/common/rfb/VNCServerST.cxx
index 51cb86c..199524e 100644
--- a/common/rfb/VNCServerST.cxx
+++ b/common/rfb/VNCServerST.cxx
@@ -544,7 +544,7 @@
   if (!deferPending)
     return true;
 
-  if (msSince(&deferStart) >= deferUpdateTime)
+  if (msSince(&deferStart) >= (unsigned)deferUpdateTime)
     return true;
 
   return false;