RustPython
diff --git a/‎crates/vm/src/builtins/type.rs‎
Lines changed: 14 additions & 4 deletions b/‎crates/vm/src/builtins/type.rs‎
Lines changed: 14 additions & 4 deletions
@@ -592,12 +592,12 @@ impl PyType {
             slots.flags |= PyTypeFlags::HAS_DICT
         }
 
-        // Inherit HAS_WEAKREF from any base in MRO that has it
+        // Inherit HAS_WEAKREF/MANAGED_WEAKREF from any base in MRO that has it
         if mro
             .iter()
             .any(|b| b.slots.flags.has_feature(PyTypeFlags::HAS_WEAKREF))
         {
-            slots.flags |= PyTypeFlags::HAS_WEAKREF
+            slots.flags |= PyTypeFlags::HAS_WEAKREF | PyTypeFlags::MANAGED_WEAKREF
         }
 
         // Inherit SEQUENCE and MAPPING flags from base classes
@@ -612,6 +612,11 @@ impl PyType {
 
         Self::inherit_readonly_slots(&mut slots, &base);
 
+        // Normalize: any type with HAS_WEAKREF gets MANAGED_WEAKREF
+        if slots.flags.has_feature(PyTypeFlags::HAS_WEAKREF) {
+            slots.flags |= PyTypeFlags::MANAGED_WEAKREF;
+        }
+
         if let Some(qualname) = attrs.get(identifier!(ctx, __qualname__))
             && !qualname.fast_isinstance(ctx.types.str_type)
         {
@@ -662,7 +667,7 @@ impl PyType {
             slots.flags |= PyTypeFlags::HAS_DICT
         }
         if base.slots.flags.has_feature(PyTypeFlags::HAS_WEAKREF) {
-            slots.flags |= PyTypeFlags::HAS_WEAKREF
+            slots.flags |= PyTypeFlags::HAS_WEAKREF | PyTypeFlags::MANAGED_WEAKREF
         }
 
         // Inherit SEQUENCE and MAPPING flags from base class
@@ -675,6 +680,11 @@ impl PyType {
 
         Self::inherit_readonly_slots(&mut slots, &base);
 
+        // Normalize: any type with HAS_WEAKREF gets MANAGED_WEAKREF
+        if slots.flags.has_feature(PyTypeFlags::HAS_WEAKREF) {
+            slots.flags |= PyTypeFlags::MANAGED_WEAKREF;
+        }
+
         let bases = PyRwLock::new(vec![base.clone()]);
         let mro = base.mro_map_collect(|x| x.to_owned());
 
@@ -1989,7 +1999,7 @@ impl Constructor for PyType {
         // 2. __weakref__ is in __slots__
         let may_add_weakref = !base.slots.flags.has_feature(PyTypeFlags::HAS_WEAKREF);
         if (heaptype_slots.is_none() && may_add_weakref) || add_weakref {
-            flags |= PyTypeFlags::HAS_WEAKREF;
+            flags |= PyTypeFlags::HAS_WEAKREF | PyTypeFlags::MANAGED_WEAKREF;
         }
 
         let (slots, heaptype_ext) = {