python · MazinSharaf · Apr 7, 2026 · Apr 7, 2026 · Apr 7, 2026 · Apr 8, 2026
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-04-08-02-49-07.gh-issue-148189.0KpXID.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-04-08-02-49-07.gh-issue-148189.0KpXID.rst
@@ -0,0 +1 @@
+Repaired undercount of bytes in type-specific free lists reported by sys._debugmallocstats(). For types that participate in cyclic garbage collection, it was missing two pointers used by GC.
@@ -443,7 +443,7 @@ _PyDict_DebugMallocStats(FILE *out)
 {
     _PyDebugAllocatorStats(out, "free PyDictObject",
                            _Py_FREELIST_SIZE(dicts),
-                           sizeof(PyDictObject));
+                           _PyType_PreHeaderSize(&PyDict_Type) + sizeof(PyDictObject));
     _PyDebugAllocatorStats(out, "free PyDictKeysObject",
                            _Py_FREELIST_SIZE(dictkeys),
                            sizeof(PyDictKeysObject));

diff --git a/Objects/listobject.c b/Objects/listobject.c
@@ -234,7 +234,7 @@ _PyList_DebugMallocStats(FILE *out)
     _PyDebugAllocatorStats(out,
                            "free PyListObject",
                             _Py_FREELIST_SIZE(lists),
-                           sizeof(PyListObject));
+                           _PyType_PreHeaderSize(&PyList_Type) + sizeof(PyListObject));
 }
 
 PyObject *
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Repaired undercount of bytes in type-specific free lists reported by sys._debugmallocstats(). For types that participate in cyclic garbage collection, it was missing two pointers used by GC.