diff --git a/layout/xul/nsSliderFrame.cpp b/layout/xul/nsSliderFrame.cpp
index d798bb3c888..5b904b7d745 100644
--- a/layout/xul/nsSliderFrame.cpp
+++ b/layout/xul/nsSliderFrame.cpp
@@ -903,7 +903,7 @@ nsSliderMediator::HandleEvent(nsIDOMEvent* aEvent)
 }
 
 bool
-nsSliderFrame::StartAPZDrag(WidgetGUIEvent* aEvent)
+nsSliderFrame::StartAPZDrag()
 {
   if (!gfxPlatform::GetPlatform()->SupportsApzDragInput()) {
     return false;
@@ -1020,7 +1020,7 @@ nsSliderFrame::StartDrag(nsIDOMEvent* aEvent)
 
   mDragStart = pos - mThumbStart;
 
-  mScrollingWithAPZ = StartAPZDrag(event);
+  mScrollingWithAPZ = StartAPZDrag();
 
 #ifdef DEBUG_SLIDER
   printf("Pressed mDragStart=%d\n",mDragStart);
diff --git a/layout/xul/nsSliderFrame.h b/layout/xul/nsSliderFrame.h
index f7d2bf49941..2b55a949cc0 100644
--- a/layout/xul/nsSliderFrame.h
+++ b/layout/xul/nsSliderFrame.h
@@ -100,7 +100,7 @@ public:
   nsresult StartDrag(nsIDOMEvent* aEvent);
   nsresult StopDrag();
 
-  bool StartAPZDrag(mozilla::WidgetGUIEvent* aEvent);
+  bool StartAPZDrag();
 
   static int32_t GetCurrentPosition(nsIContent* content);
   static int32_t GetMinPosition(nsIContent* content);