pythoncapi
diff --git a/‎Doc/c-api/gcsupport.rst‎
Lines changed: 1 addition & 1 deletion b/‎Doc/c-api/gcsupport.rst‎
Lines changed: 1 addition & 1 deletion
diff --git a/‎Modules/gcmodule.c‎
Lines changed: 1 addition & 0 deletions b/‎Modules/gcmodule.c‎
Lines changed: 1 addition & 0 deletions
@@ -49,7 +49,7 @@ Constructors for container types must conform to two rules:
 .. c:function:: TYPE* PyObject_GC_Resize(TYPE, PyVarObject *op, Py_ssize_t newsize)
 
    Resize an object allocated by :c:func:`PyObject_NewVar`.  Returns the
-   resized object or *NULL* on failure.
+   resized object or *NULL* on failure.  *op* must not be tracked by the collector yet.
 
 
 .. c:function:: void PyObject_GC_Track(PyObject *op)
 
@@ -1752,6 +1752,7 @@ _PyObject_GC_Resize(PyVarObject *op, Py_ssize_t nitems)
 {
     const size_t basicsize = _PyObject_VAR_SIZE(Py_TYPE(op), nitems);
     PyGC_Head *g = AS_GC(op);
+    assert(!IS_TRACKED(op));
     if (basicsize > PY_SSIZE_T_MAX - sizeof(PyGC_Head))
         return (PyVarObject *)PyErr_NoMemory();
     g = (PyGC_Head *)PyObject_REALLOC(g,  sizeof(PyGC_Head) + basicsize);
Original file line number	Diff line number	Diff line change
`@@ -1752,6 +1752,7 @@ _PyObject_GC_Resize(PyVarObject *op, Py_ssize_t nitems)`
`1752`	`1752`	`{`
`1753`	`1753`	`const size_t basicsize = _PyObject_VAR_SIZE(Py_TYPE(op), nitems);`
`1754`	`1754`	`PyGC_Head *g = AS_GC(op);`
	`1755`	`+ assert(!IS_TRACKED(op));`
`1755`	`1756`	`if (basicsize > PY_SSIZE_T_MAX - sizeof(PyGC_Head))`
`1756`	`1757`	`return (PyVarObject *)PyErr_NoMemory();`
`1757`	`1758`	`g = (PyGC_Head *)PyObject_REALLOC(g, sizeof(PyGC_Head) + basicsize);`