diff --git a/js/src/xpconnect/src/xpcprivate.h b/js/src/xpconnect/src/xpcprivate.h
index 7e676ffa4db..d1c0e8af62e 100644
--- a/js/src/xpconnect/src/xpcprivate.h
+++ b/js/src/xpconnect/src/xpcprivate.h
@@ -1371,6 +1371,7 @@ private:
     nsDeque*          mJSContextStack;
     JSContext*        mSafeJSContext;
     xpcPerThreadData* mNextThread;
+    PRBool            mSafeContextIsFromSetter;
 
     static PRLock*           gLock;
     static xpcPerThreadData* gThreads;
diff --git a/js/src/xpconnect/src/xpcthreadcontext.cpp b/js/src/xpconnect/src/xpcthreadcontext.cpp
index bf3f2c0430b..f59a0a0deab 100644
--- a/js/src/xpconnect/src/xpcthreadcontext.cpp
+++ b/js/src/xpconnect/src/xpcthreadcontext.cpp
@@ -198,7 +198,8 @@ xpcPerThreadData::xpcPerThreadData()
     :   mException(nsnull),
         mJSContextStack(new nsDeque(nsnull)),
         mSafeJSContext(nsnull),
-        mNextThread(nsnull)
+        mNextThread(nsnull),
+        mSafeContextIsFromSetter(PR_FALSE)
 {
     if(gLock)
     {
@@ -219,7 +220,7 @@ xpcPerThreadData::Cleanup()
         mJSContextStack = nsnull;
     }
 
-    if(mSafeJSContext)
+    if(mSafeJSContext && !mSafeContextIsFromSetter)
     {
         JS_DestroyContext(mSafeJSContext);
         mSafeJSContext = nsnull;
@@ -328,8 +329,8 @@ xpcPerThreadData::GetSafeJSContext()
 nsresult
 xpcPerThreadData::SetSafeJSContext(JSContext *cx)
 {
-    NS_ASSERTION(!mSafeJSContext, "SetSafeJSContext called too late!");
     mSafeJSContext = cx;
+    mSafeContextIsFromSetter = PR_TRUE;
     return NS_OK;
 }