diff --git a/common/rfb/Congestion.cxx b/common/rfb/Congestion.cxx
index 4a78452..f3f9cee 100644
--- a/common/rfb/Congestion.cxx
+++ b/common/rfb/Congestion.cxx
@@ -70,7 +70,7 @@
 
 // Compare position even when wrapped around
 static inline bool isAfter(unsigned a, unsigned b) {
-  return (int)a - (int)b > 0;
+  return a != b && a - b <= UINT_MAX / 2;
 }
 
 static LogWriter vlog("Congestion");