diff --git a/refs.c b/refs.c
index d6bdb47ad6..010ed07e33 100644
--- a/refs.c
+++ b/refs.c
@@ -273,6 +273,12 @@ static void add_entry_to_dir(struct ref_dir *dir, struct ref_entry *entry)
 {
 	ALLOC_GROW(dir->entries, dir->nr + 1, dir->alloc);
 	dir->entries[dir->nr++] = entry;
+	/* optimize for the case that entries are added in order */
+	if (dir->nr == 1 ||
+	    (dir->nr == dir->sorted + 1 &&
+	     strcmp(dir->entries[dir->nr - 2]->name,
+		    dir->entries[dir->nr - 1]->name) < 0))
+		dir->sorted = dir->nr;
 }
 
 /*