diff --git a/src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Controls/PopupControlService.cs b/src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Controls/PopupControlService.cs
index 952fa101ade..1d51ae30aa3 100644
--- a/src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Controls/PopupControlService.cs
+++ b/src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Controls/PopupControlService.cs
@@ -330,7 +330,7 @@ private void BeginShowToolTip(DependencyObject o, ToolTipService.TriggerAction t
                 switch (triggerAction)
                 {
                     case ToolTipService.TriggerAction.Mouse:
-                        if (SafeArea != null)
+                        if (HasValidSafeArea)
                         {
                             // the mouse has moved over a tooltip owner o, while still
                             // within the safe area of the current tooltip (which must be from mouse).
@@ -909,8 +909,8 @@ private void SetSafeArea(ToolTip tooltip)
 
         private bool MouseHasLeftSafeArea()
         {
-            // if there is no SafeArea, the mouse didn't leave it
-            if (SafeArea == null)
+            // if there is no valid SafeArea, the mouse didn't leave it
+            if (!HasValidSafeArea)
                 return false;
 
             // if the current tooltip's owner is no longer being displayed, the safe area is no longer valid
@@ -926,6 +926,17 @@ private bool MouseHasLeftSafeArea()
 
         private ConvexHull SafeArea { get; set; }
 
+        private bool HasValidSafeArea
+        {
+            get
+            {
+                // There are plenty of Watsons which indicate that source might get disposed
+                // (i.e. underlying HWND gets destroyed) while we are still holding on it.
+                // If such a case treat it as if there is no valid safe area.
+                return SafeArea != null && SafeArea.IsValid;
+            }
+        }
+
         #endregion
 
         #endregion
@@ -1374,6 +1385,8 @@ internal ConvexHull(PresentationSource source, List<NativeMethods.RECT> rects)
                 }
             }
 
+            internal bool IsValid => !_source.IsDisposed;
+
             // sort by y (and by x among equal y's)
             private void SortPoints(PointList points)
             {