diff --git a/Include/object.h b/Include/object.h
index a2aadb6..b4b9ce2 100644
--- a/Include/object.h
+++ b/Include/object.h
@@ -532,6 +532,9 @@
 #define Py_TPFLAGS_HAVE_VERSION_TAG   (1L<<18)
 #define Py_TPFLAGS_VALID_VERSION_TAG  (1L<<19)
 
+/* Type is abstract and cannot be instantiated */
+#define Py_TPFLAGS_IS_ABSTRACT (1L<<20)
+
 /* These flags are used to determine if a type is a subclass. */
 #define Py_TPFLAGS_INT_SUBCLASS		(1L<<23)
 #define Py_TPFLAGS_LONG_SUBCLASS	(1L<<24)