diff --git a/mercurial/cext/revlog.c b/mercurial/cext/revlog.c
--- a/mercurial/cext/revlog.c
+++ b/mercurial/cext/revlog.c
@@ -1535,7 +1535,7 @@ static PyObject *find_deepest(indexObjec
 		goto bail;
 	}
 
-	interesting = calloc(sizeof(*interesting), 1 << revcount);
+	interesting = calloc(sizeof(*interesting), ((size_t)1) << revcount);
 	if (interesting == NULL) {
 		PyErr_NoMemory();
 		goto bail;