diff --git a/AK/OwnPtr.h b/AK/OwnPtr.h
index 874f468751..67a19578db 100644
--- a/AK/OwnPtr.h
+++ b/AK/OwnPtr.h
@@ -46,6 +46,10 @@ public:
     template<typename U>
     OwnPtr& operator=(const OwnPtr<U>&) = delete;
 
+    template<typename U>
+    OwnPtr(const NonnullOwnPtr<U>&) = delete;
+    template<typename U>
+    OwnPtr& operator=(const NonnullOwnPtr<U>&) = delete;
     template<typename U>
     OwnPtr(const RefPtr<U>&) = delete;
     template<typename U>