1 files changed, 9 insertions, 4 deletions
diff --git a/Python/sysmodule.c b/Python/sysmodule.c
index 5cab149..407d770 100644
--- a/Python/sysmodule.c
+++ b/Python/sysmodule.c
@@ -689,7 +689,7 @@ _PySys_GetSizeOf(PyObject *o)
 {
     static PyObject *str__sizeof__ = NULL;
     PyObject *res = NULL;
-    size_t size;
+    Py_ssize_t size;
 
     /* Make sure the type is initialized. float gets initialized late */
     if (PyType_Ready(Py_TYPE(o)) < 0)
@@ -718,14 +718,19 @@ _PySys_GetSizeOf(PyObject *o)
 
         size = (size_t)PyInt_AsSsize_t(res);
         Py_DECREF(res);
-        if (size == (size_t)-1 && PyErr_Occurred())
+        if (size == -1 && PyErr_Occurred())
             return (size_t)-1;
     }
 
+    if (size < 0) {
+        PyErr_SetString(PyExc_ValueError, "__sizeof__() should return >= 0");
+        return (size_t)-1;
+    }
+
     /* add gc_head size */
     if (PyObject_IS_GC(o))
-        size += sizeof(PyGC_Head);
-    return size;
+        return ((size_t)size) + sizeof(PyGC_Head);
+    return (size_t)size;
 }
 
 static PyObject *