--- a/mercurial/cext/parsers.c	Mon Apr 08 10:52:04 2019 -0400
+++ b/mercurial/cext/parsers.c	Tue Apr 09 21:59:37 2019 +0900
@@ -184,7 +184,8 @@
 		goto quit;
 	}
 
-	parents = Py_BuildValue(PY23("s#s#", "y#y#"), str, 20, str + 20, 20);
+	parents = Py_BuildValue(PY23("s#s#", "y#y#"), str, (Py_ssize_t)20,
+	                        str + 20, (Py_ssize_t)20);
 	if (!parents) {
 		goto quit;
 	}