diff --git a/Include/pydebug.h b/Include/pydebug.h
index db3b656..3282dc1 100644
--- a/Include/pydebug.h
+++ b/Include/pydebug.h
@@ -21,6 +21,8 @@
   on the command line, and is used in 2.2 by ceval.c to make all "/" divisions
   true divisions (which they will be in 3.0). */
 PyAPI_DATA(int) _Py_QnewFlag;
+/* Warn about 3.x issues */
+PyAPI_DATA(int) Py_Py3kWarningFlag;
 
 /* this is a wrapper around getenv() that pays attention to
    Py_IgnoreEnvironmentFlag.  It should be used for getting variables like