diff --git a/mozilla/layout/base/nsPresShell.cpp b/mozilla/layout/base/nsPresShell.cpp
index 2a6d48a3f97..a9339683401 100644
--- a/mozilla/layout/base/nsPresShell.cpp
+++ b/mozilla/layout/base/nsPresShell.cpp
@@ -5409,7 +5409,7 @@ PresShell::HandleEvent(nsIView         *aView,
 
     nsPresContext* framePresContext = frame->PresContext();
     nsPresContext* rootPresContext = framePresContext->RootPresContext();
-    NS_ASSERTION(rootPresContext = mPresContext->RootPresContext(),
+    NS_ASSERTION(rootPresContext == mPresContext->RootPresContext(),
                  "How did we end up outside the connected prescontext/viewmanager hierarchy?"); 
     // If we aren't starting our event dispatch from the root frame of the root prescontext,
     // then someone must be capturing the mouse. In that case we don't want to search the popup