diff --git a/base/src/mac/nsRepeater.cpp b/base/src/mac/nsRepeater.cpp
index cbabf95d3873..5a93b4d29705 100644
--- a/base/src/mac/nsRepeater.cpp
+++ b/base/src/mac/nsRepeater.cpp
@@ -39,6 +39,7 @@ Repeater::~Repeater()
 
 // protected helper functs
 
+//----------------------------------------------------------------------------
 void Repeater::AddToRepeatList()
 {
   if (sRepeaters)
@@ -48,6 +49,8 @@ void Repeater::AddToRepeatList()
   }
   sRepeaters = this;
 }
+
+//----------------------------------------------------------------------------
 void Repeater::RemoveFromRepeatList()
 {
   if (sRepeaters == this) sRepeaters = mNextRptr;
@@ -56,18 +59,22 @@ void Repeater::RemoveFromRepeatList()
   mPrevRptr = 0;
   mNextRptr = 0;
 }
+
+//----------------------------------------------------------------------------
 void Repeater::AddToIdleList()
 {
-  if (sRepeaters)
+  if (sIdlers)
   {
-    sRepeaters->mPrevIdlr = this;
-    mNextIdlr = sRepeaters;
+    sIdlers->mPrevIdlr = this;
+    mNextIdlr = sIdlers;
   }
-  sRepeaters = this;
+  sIdlers = this;
 }
+
+//----------------------------------------------------------------------------
 void Repeater::RemoveFromIdleList()
 {
-  if (sRepeaters == this) sRepeaters = mNextIdlr;
+  if (sIdlers == this) sIdlers = mNextIdlr;
   if (mPrevIdlr) mPrevIdlr->mNextIdlr = mNextIdlr;
   if (mNextIdlr) mNextIdlr->mPrevIdlr = mPrevIdlr;
   mPrevIdlr = 0;
@@ -75,6 +82,7 @@ void Repeater::RemoveFromIdleList()
 }
 
 // repeater methods
+//----------------------------------------------------------------------------
 
 void Repeater::StartRepeating()
 {
diff --git a/base/src/mac/nsTimerMac.cpp b/base/src/mac/nsTimerMac.cpp
index b1bea49f6668..e1f17eaa64ec 100644
--- a/base/src/mac/nsTimerMac.cpp
+++ b/base/src/mac/nsTimerMac.cpp
@@ -77,9 +77,23 @@ class TimerImpl : public nsITimer
 
     virtual void* GetClosure();
   
+#if DEBUG
+	enum {
+		eGoodTimerSignature = 'Barf',
+		eDeletedTimerSignature = 'oops'
+	};
+	
+  	Boolean			IsGoodTimer() { return (mSignature == eGoodTimerSignature); }
+#endif
+  	
   private:
   // Calculates mFireTime too
     void SetDelaySelf( PRUint32 aDelay );
+    
+#if DEBUG
+    UInt32		mSignature;
+#endif
+
 };
 
 #pragma mark class TimerPeriodical
@@ -126,6 +140,7 @@ TimerImpl::TimerImpl()
 ,  mClosure(nsnull)
 ,  mDelay(0)
 ,  mFireTime(0)
+,  mSignature(eGoodTimerSignature)
 {
   NS_INIT_REFCNT();
 }
@@ -136,6 +151,7 @@ TimerImpl::~TimerImpl()
 {
   Cancel();
   NS_IF_RELEASE(mCallbackObject);
+  mSignature = eDeletedTimerSignature;
 }
 
 //----------------------------------------------------------------------------------------
@@ -265,7 +281,10 @@ void  TimerPeriodical::RepeatAction( const EventRecord &inMacEvent)
   
   while (iter != mTimers.end())
   {
-    TimerImpl* timer = *iter; 
+    TimerImpl* timer = *iter;
+    
+    NS_ASSERTION(timer->IsGoodTimer(), "Bad timer!");
+    
     if (timer->GetFireTime() <= inMacEvent.when)
     {
       mTimers.erase(iter++);