diff --git a/builtin-receive-pack.c b/builtin-receive-pack.c
index bb34757d27..7e4129ddc8 100644
--- a/builtin-receive-pack.c
+++ b/builtin-receive-pack.c
@@ -515,9 +515,9 @@ static void check_aliased_update(struct command *cmd, struct string_list *list)
 	dst_cmd->skip_update = 1;
 
 	strcpy(cmd_oldh, find_unique_abbrev(cmd->old_sha1, DEFAULT_ABBREV));
-	strcat(cmd_newh, find_unique_abbrev(cmd->new_sha1, DEFAULT_ABBREV));
+	strcpy(cmd_newh, find_unique_abbrev(cmd->new_sha1, DEFAULT_ABBREV));
 	strcpy(dst_oldh, find_unique_abbrev(dst_cmd->old_sha1, DEFAULT_ABBREV));
-	strcat(dst_newh, find_unique_abbrev(dst_cmd->new_sha1, DEFAULT_ABBREV));
+	strcpy(dst_newh, find_unique_abbrev(dst_cmd->new_sha1, DEFAULT_ABBREV));
 	rp_error("refusing inconsistent update between symref '%s' (%s..%s) and"
 		 " its target '%s' (%s..%s)",
 		 cmd->ref_name, cmd_oldh, cmd_newh,