diff --git a/Xi/exevents.c b/Xi/exevents.c
index 753172c0e..b8e2c489f 100644
--- a/Xi/exevents.c
+++ b/Xi/exevents.c
@@ -3242,8 +3242,11 @@ DeviceEventSuppressForWindow(WindowPtr pWin, ClientPtr client, Mask mask,
         inputMasks->dontPropagateMask[maskndx] = mask;
     }
     RecalculateDeviceDeliverableEvents(pWin);
-    if (ShouldFreeInputMasks(pWin, FALSE))
+    if (ShouldFreeInputMasks(pWin, FALSE)) {
+        BUG_RETURN_VAL(!inputMasks, BadImplementation);
+        BUG_RETURN_VAL(!inputMasks->inputClients, BadImplementation);
         FreeResource(inputMasks->inputClients->resource, X11_RESTYPE_NONE);
+    }
     return Success;
 }