diff --git a/python/enum.c b/python/enum.c
index dfe1b1e..2084739 100644
--- a/python/enum.c
+++ b/python/enum.c
@@ -52,7 +52,7 @@ enumitem_new (PyTypeObject *type,
 
     /* we assume the "fast path" for a single-digit ints (see longobject.c) */
     /* this also holds if we get a small_int preallocated long */
-    Py_SIZE(&self->val) = Py_SIZE(longval);
+    Py_SET_SIZE(&self->val, Py_SIZE(longval));
     self->val.ob_digit[0] = longval->ob_digit[0];
     Py_DECREF(longval);
 #else
@@ -143,7 +143,7 @@ zbarEnumItem_New (PyObject *byname,
 
     /* we assume the "fast path" for a single-digit ints (see longobject.c) */
     /* this also holds if we get a small_int preallocated long */
-    Py_SIZE(&self->val) = Py_SIZE(longval);
+    Py_SET_SIZE(&self->val, Py_SIZE(longval));
     self->val.ob_digit[0] = longval->ob_digit[0];
     Py_DECREF(longval);