diff --git a/strbuf.c b/strbuf.c
index b0716ac585..030556111d 100644
--- a/strbuf.c
+++ b/strbuf.c
@@ -921,7 +921,7 @@ void strbuf_add_unique_abbrev(struct strbuf *sb, const struct object_id *oid,
 			      int abbrev_len)
 {
 	int r;
-	strbuf_grow(sb, GIT_SHA1_HEXSZ + 1);
+	strbuf_grow(sb, GIT_MAX_HEXSZ + 1);
 	r = find_unique_abbrev_r(sb->buf + sb->len, oid, abbrev_len);
 	strbuf_setlen(sb, sb->len + r);
 }