1 files changed, 1 insertions, 1 deletions
diff --git a/Parser/parsetok.c b/Parser/parsetok.c
index 00d741d..b9c9fe8 100644
--- a/Parser/parsetok.c
+++ b/Parser/parsetok.c
@@ -225,7 +225,7 @@ parsetok(struct tok_state *tok, grammar *g, int start, perrdetail *err_ret,
         }
         else
             started = 1;
-        len = b - a; /* XXX this may compute NULL - NULL */
+        len = (a != NULL && b != NULL) ? b - a : 0;
         str = (char *) PyObject_MALLOC(len + 1);
         if (str == NULL) {
             err_ret->error = E_NOMEM;