diff --git a/Doc/c-api/typeobj.rst b/Doc/c-api/typeobj.rst
index 8bd3144f88aa71..e9609dfaab59f3 100644
--- a/Doc/c-api/typeobj.rst
+++ b/Doc/c-api/typeobj.rst
@@ -1260,7 +1260,7 @@ and :c:data:`PyType_Type` effectively act as defaults.)
       This bit indicates that instances of the class have a :attr:`~object.__dict__`
       attribute, and that the space for the dictionary is managed by the VM.
 
-      If this flag is set, :c:macro:`Py_TPFLAGS_HAVE_GC` should also be set.
+      If this flag is set, :c:macro:`Py_TPFLAGS_HAVE_GC` must also be set.
 
       The type traverse function must call :c:func:`PyObject_VisitManagedDict`
       and its clear function must call :c:func:`PyObject_ClearManagedDict`.
@@ -1278,6 +1278,8 @@ and :c:data:`PyType_Type` effectively act as defaults.)
       This bit indicates that instances of the class should be weakly
       referenceable.
 
+      If this flag is set, :c:macro:`Py_TPFLAGS_HAVE_GC` must also be set.
+
       .. versionadded:: 3.12
 
       **Inheritance:**
diff --git a/Doc/extending/newtypes.rst b/Doc/extending/newtypes.rst
index e3612f3a1875ca..26085b5cebd3ad 100644
--- a/Doc/extending/newtypes.rst
+++ b/Doc/extending/newtypes.rst
@@ -560,6 +560,8 @@ For an object to be weakly referenceable, the extension type must set the
 field. The legacy :c:member:`~PyTypeObject.tp_weaklistoffset` field should
 be left as zero.
 
+If this flag is set, :c:macro:`Py_TPFLAGS_HAVE_GC` should also be set.
+
 Concretely, here is how the statically declared type object would look::
 
    static PyTypeObject TrivialType = {
diff --git a/Doc/whatsnew/3.15.rst b/Doc/whatsnew/3.15.rst
index fc5519286e2264..b03017f17d64df 100644
--- a/Doc/whatsnew/3.15.rst
+++ b/Doc/whatsnew/3.15.rst
@@ -803,6 +803,14 @@ New features
   (Contributed by Victor Stinner in :gh:`129813`.)
 
 
+Changed C APIs
+--------------
+
+* If the :c:macro:`Py_TPFLAGS_MANAGED_DICT` and :c:macro:`Py_TPFLAGS_MANAGED_WEAKREF`
+  flags are set then :c:macro:`Py_TPFLAGS_HAVE_GC` must be set too.
+  (Contributed by Sergey Miryanov in :gh:`134786`)
+
+
 Porting to Python 3.15
 ----------------------
 
diff --git a/Include/object.h b/Include/object.h
index 9585f4a1d67a52..117d057a18178f 100644
--- a/Include/object.h
+++ b/Include/object.h
@@ -529,7 +529,7 @@ given type object has a specified feature.
 #define Py_TPFLAGS_INLINE_VALUES (1 << 2)
 
 /* Placement of weakref pointers are managed by the VM, not by the type.
- * The VM will automatically set tp_weaklistoffset.
+ * The VM will automatically set tp_weaklistoffset. Implies Py_TPFLAGS_HAVE_GC.
  */
 #define Py_TPFLAGS_MANAGED_WEAKREF (1 << 3)
 
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-06-24-13-12-58.gh-issue-134786.MF0VVk.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-06-24-13-12-58.gh-issue-134786.MF0VVk.rst
new file mode 100644
index 00000000000000..664e4d2db384ad
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2025-06-24-13-12-58.gh-issue-134786.MF0VVk.rst
@@ -0,0 +1,2 @@
+If :c:macro:`Py_TPFLAGS_MANAGED_DICT` and :c:macro:`Py_TPFLAGS_MANAGED_WEAKREF`
+are used, then :c:macro:`Py_TPFLAGS_HAVE_GC` must be used as well.
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index 7d03655e77a0bb..9e1b428422f0dc 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -8893,6 +8893,13 @@ type_ready_preheader(PyTypeObject *type)
                         type->tp_name);
             return -1;
         }
+        if (!(type->tp_flags & Py_TPFLAGS_HAVE_GC)) {
+            PyErr_Format(PyExc_SystemError,
+                        "type %s has the Py_TPFLAGS_MANAGED_DICT flag "
+                        "but not Py_TPFLAGS_HAVE_GC flag",
+                        type->tp_name);
+            return -1;
+        }
         type->tp_dictoffset = -1;
     }
     if (type->tp_flags & Py_TPFLAGS_MANAGED_WEAKREF) {
@@ -8905,6 +8912,13 @@ type_ready_preheader(PyTypeObject *type)
                         type->tp_name);
             return -1;
         }
+        if (!(type->tp_flags & Py_TPFLAGS_HAVE_GC)) {
+            PyErr_Format(PyExc_SystemError,
+                        "type %s has the Py_TPFLAGS_MANAGED_WEAKREF flag "
+                        "but not Py_TPFLAGS_HAVE_GC flag",
+                        type->tp_name);
+            return -1;
+        }
         type->tp_weaklistoffset = MANAGED_WEAKREF_OFFSET;
     }
     return 0;