--- a/mercurial/parsers.c	Thu Aug 06 22:11:20 2015 -0700
+++ b/mercurial/parsers.c	Tue Aug 11 14:49:40 2015 -0400
@@ -1143,8 +1143,10 @@
 
 	/* Initialize return set */
 	reachable = PySet_New(0);
-	if (reachable == NULL)
+	if (reachable == NULL) {
+		PyErr_NoMemory();
 		goto bail;
+	}
 
 	/* Initialize internal datastructures */
 	tovisit = (int *)malloc((len + 1) * sizeof(int));