diff --git a/Parser/pgen.c b/Parser/pgen.c
index 03d3c826dad..f3fdb46d1e1 100644
--- a/Parser/pgen.c
+++ b/Parser/pgen.c
@@ -13,7 +13,7 @@
 #include "pgen.h"
 
 extern int Py_DebugFlag;
-int Py_IgnoreEnvironmentFlag; /* needed by Py_GETENV */
+extern int Py_IgnoreEnvironmentFlag; /* needed by Py_GETENV */
 
 
 /* PART ONE -- CONSTRUCT NFA -- Cf. Algorithm 3.2 from [Aho&Ullman 77] */