diff --git a/widget/MouseEvents.h b/widget/MouseEvents.h
index c913af29951..f4056c67010 100644
--- a/widget/MouseEvents.h
+++ b/widget/MouseEvents.h
@@ -94,7 +94,6 @@ public:
   virtual WidgetEvent* Duplicate() const override
   {
     MOZ_CRASH("WidgetMouseEventBase must not be most-subclass");
-    return nullptr;
   }
 
   /// The possible related target
diff --git a/widget/TextEvents.h b/widget/TextEvents.h
index 53a4fe1bd5c..15f112ac3d1 100644
--- a/widget/TextEvents.h
+++ b/widget/TextEvents.h
@@ -489,7 +489,6 @@ public:
     NS_ASSERTION(!IsAllowedToDispatchDOMEvent(),
       "WidgetQueryContentEvent needs to support Duplicate()");
     MOZ_CRASH("WidgetQueryContentEvent doesn't support Duplicate()");
-    return nullptr;
   }
 
   void InitForQueryTextContent(uint32_t aOffset, uint32_t aLength,
diff --git a/widget/WidgetUtils.cpp b/widget/WidgetUtils.cpp
index fe15181d021..95bbb8475f4 100644
--- a/widget/WidgetUtils.cpp
+++ b/widget/WidgetUtils.cpp
@@ -92,7 +92,6 @@ nsIntRect RotateRect(nsIntRect aRect,
                        aRect.height, aRect.width);
     default:
       MOZ_CRASH("Unknown rotation");
-      return aRect;
   }
 }
 
diff --git a/widget/tests/TestAppShellSteadyState.cpp b/widget/tests/TestAppShellSteadyState.cpp
index 8156335c97a..b7e05a976c0 100644
--- a/widget/tests/TestAppShellSteadyState.cpp
+++ b/widget/tests/TestAppShellSteadyState.cpp
@@ -391,8 +391,7 @@ Test4Internal(nsIAppShell* aAppShell)
 #ifndef XP_WIN
   // Not sure how to test on other platforms.
   return false;
-#endif
-
+#else
   nsCOMPtr<nsIAppShellService> appService =
     do_GetService(NS_APPSHELLSERVICE_CONTRACTID);
   if (!appService) {
@@ -437,6 +436,7 @@ Test4Internal(nsIAppShell* aAppShell)
   }
 
   return true;
+#endif
 }
 
 void