diff --git a/widget/src/windows/nsWindow.cpp b/widget/src/windows/nsWindow.cpp
index 5c348802e706..10f14f6ac1ac 100644
--- a/widget/src/windows/nsWindow.cpp
+++ b/widget/src/windows/nsWindow.cpp
@@ -400,6 +400,7 @@ nsWindow::nsWindow() : nsBaseWidget()
   mCustomNonClient      = PR_FALSE;
   mHideChrome           = PR_FALSE;
   mFullscreenMode       = PR_FALSE;
+  mMousePresent         = PR_FALSE;
   mWindowType           = eWindowType_child;
   mBorderStyle          = eBorderStyle_default;
   mPopupType            = ePopupTypeAny;
@@ -4921,6 +4922,8 @@ PRBool nsWindow::ProcessMessage(UINT msg, WPARAM &wParam, LPARAM &lParam,
       // priority
       SetTimer(mWnd, KILL_PRIORITY_ID, 2000 /* 2seconds */, NULL);
 #endif
+      mMousePresent = PR_TRUE;
+
       // Suppress dispatch of pending events
       // when mouse moves are generated by widget
       // creation instead of user input.
@@ -4942,6 +4945,13 @@ PRBool nsWindow::ProcessMessage(UINT msg, WPARAM &wParam, LPARAM &lParam,
     }
     break;
 
+    case WM_NCMOUSEMOVE:
+      // If we receive a mouse move event on non-client chrome, make sure and
+      // send an NS_MOUSE_EXIT event as well.
+      if (mMousePresent && !mIsInMouseCapture)
+        SendMessage(mWnd, WM_MOUSELEAVE, 0, 0);
+    break;
+
 #ifdef WINCE_WINDOWS_MOBILE
     case WM_TIMER:
       SetThreadPriority(GetCurrentThread(), THREAD_PRIORITY_NORMAL);
@@ -4977,6 +4987,10 @@ PRBool nsWindow::ProcessMessage(UINT msg, WPARAM &wParam, LPARAM &lParam,
 #ifndef WINCE
     case WM_MOUSELEAVE:
     {
+      if (!mMousePresent)
+        break;
+      mMousePresent = PR_FALSE;
+
       // We need to check mouse button states and put them in for
       // wParam.
       WPARAM mouseState = (GetKeyState(VK_LBUTTON) ? MK_LBUTTON : 0)
diff --git a/widget/src/windows/nsWindow.h b/widget/src/windows/nsWindow.h
index 96bd5e0b62e2..3cf566633807 100644
--- a/widget/src/windows/nsWindow.h
+++ b/widget/src/windows/nsWindow.h
@@ -500,6 +500,7 @@ protected:
   PRPackedBool          mHideChrome;
   PRPackedBool          mIsRTL;
   PRPackedBool          mFullscreenMode;
+  PRPackedBool          mMousePresent;
   PRUint32              mBlurSuppressLevel;
   DWORD_PTR             mOldStyle;
   DWORD_PTR             mOldExStyle;