diff --git a/common/rfb/DecodeManager.cxx b/common/rfb/DecodeManager.cxx
index a655c53..ccf084f 100644
--- a/common/rfb/DecodeManager.cxx
+++ b/common/rfb/DecodeManager.cxx
@@ -197,7 +197,7 @@
 {
   os::AutoMutex a(queueMutex);
 
-  if (threadException == NULL)
+  if (threadException != NULL)
     return;
 
   threadException = new rdr::Exception("Exception on worker thread: %s", e.str());