diff --git a/dev/oophm/src/com/google/gwt/dev/shell/BrowserListener.java b/dev/oophm/src/com/google/gwt/dev/shell/BrowserListener.java
index 4d6c225..b06c46a 100644
--- a/dev/oophm/src/com/google/gwt/dev/shell/BrowserListener.java
+++ b/dev/oophm/src/com/google/gwt/dev/shell/BrowserListener.java
@@ -98,6 +98,8 @@
   }
 
   public void start() {
-    listenThread.start();
+    if (listenThread != null) {
+      listenThread.start();
+    }
   }
 }