pythonnet
diff --git a/‎src/runtime/managedtype.cs
Lines changed: 19 additions & 2 deletions b/‎src/runtime/managedtype.cs
Lines changed: 19 additions & 2 deletions
diff --git a/‎src/runtime/runtime.cs
Lines changed: 5 additions & 1 deletion b/‎src/runtime/runtime.cs
Lines changed: 5 additions & 1 deletion
@@ -28,8 +28,23 @@ internal enum TrackTypes
         internal IntPtr pyHandle; // PyObject *
         internal IntPtr tpHandle; // PyType *
 
-        internal BorrowedReference ObjectReference => new(pyHandle);
-        internal BorrowedReference TypeReference => new(tpHandle);
+        internal BorrowedReference ObjectReference
+        {
+            get
+            {
+                Debug.Assert(pyHandle != IntPtr.Zero);
+                return new(pyHandle);
+            }
+        }
+
+        internal BorrowedReference TypeReference
+        {
+            get
+            {
+                Debug.Assert(tpHandle != IntPtr.Zero);
+                return new(tpHandle);
+            }
+        }
 
         private static readonly Dictionary<ManagedType, TrackTypes> _managedObjs = new Dictionary<ManagedType, TrackTypes>();
 
@@ -310,6 +325,8 @@ internal static void InitGCHandle(BorrowedReference reflectedClrObject, GCHandle
 
         internal static void SetGCHandle(BorrowedReference reflectedClrObject, BorrowedReference type, GCHandle newHandle)
         {
+            Debug.Assert(type != null);
+            Debug.Assert(reflectedClrObject != null);
             Debug.Assert(Runtime.PyObject_TypeCheck(reflectedClrObject, type));
 
             int offset = Marshal.ReadInt32(type.DangerousGetAddress(), Offsets.tp_clr_inst_offset);
 
@@ -2021,7 +2021,11 @@ internal static bool PyType_Check(IntPtr ob)
         internal static void PyType_Modified(BorrowedReference type) => Delegates.PyType_Modified(type);
         internal static bool PyType_IsSubtype(BorrowedReference t1, IntPtr ofType)
             => PyType_IsSubtype(t1, new BorrowedReference(ofType));
-        internal static bool PyType_IsSubtype(BorrowedReference t1, BorrowedReference t2) => Delegates.PyType_IsSubtype(t1, t2);
+        internal static bool PyType_IsSubtype(BorrowedReference t1, BorrowedReference t2)
+        {
+            Debug.Assert(t1 != null && t2 != null);
+            return Delegates.PyType_IsSubtype(t1, t2);
+        }
 
         internal static bool PyObject_TypeCheck(IntPtr ob, IntPtr tp)
             => PyObject_TypeCheck(new BorrowedReference(ob), new BorrowedReference(tp));