diff --git a/builtin/commit-graph.c b/builtin/commit-graph.c
index 4a70b33fb5f135..5bfba972498acb 100644
--- a/builtin/commit-graph.c
+++ b/builtin/commit-graph.c
@@ -140,7 +140,7 @@ static int graph_write(int argc, const char **argv)
 		OPT_INTEGER(0, "size-multiple", &split_opts.size_multiple,
 			N_("maximum ratio between two levels of a split commit-graph")),
 		OPT_EXPIRY_DATE(0, "expire-time", &split_opts.expire_time,
-			N_("maximum number of commits in a non-base split commit-graph")),
+			N_("only expire files older than a given date-time")),
 		OPT_END(),
 	};
 
diff --git a/commit-graph.c b/commit-graph.c
index f013a84e294b13..0d0d37787a0c35 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -1707,7 +1707,7 @@ static void expire_commit_graphs(struct write_commit_graph_context *ctx)
 	timestamp_t expire_time = time(NULL);
 
 	if (ctx->split_opts && ctx->split_opts->expire_time)
-		expire_time -= ctx->split_opts->expire_time;
+		expire_time = ctx->split_opts->expire_time;
 	if (!ctx->split) {
 		char *chain_file_name = get_chain_filename(ctx->odb);
 		unlink(chain_file_name);
diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index 43a7a66c9d1b50..6b20e60314d9e8 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -521,10 +521,10 @@ test_expect_success 'repack with minimum size does not alter existing packs' '
 		cd dup &&
 		rm -rf .git/objects/pack &&
 		mv .git/objects/pack-backup .git/objects/pack &&
-		touch -m -t 201901010000 .git/objects/pack/pack-D* &&
-		touch -m -t 201901010001 .git/objects/pack/pack-C* &&
-		touch -m -t 201901010002 .git/objects/pack/pack-B* &&
-		touch -m -t 201901010003 .git/objects/pack/pack-A* &&
+		test-tool chmtime =-5 .git/objects/pack/pack-D* &&
+		test-tool chmtime =-4 .git/objects/pack/pack-C* &&
+		test-tool chmtime =-3 .git/objects/pack/pack-B* &&
+		test-tool chmtime =-2 .git/objects/pack/pack-A* &&
 		ls .git/objects/pack >expect &&
 		MINSIZE=$(test-tool path-utils file-size .git/objects/pack/*pack | sort -n | head -n 1) &&
 		git multi-pack-index repack --batch-size=$MINSIZE &&
diff --git a/t/t5324-split-commit-graph.sh b/t/t5324-split-commit-graph.sh
index 53b2e6b4555de7..b8b208fc3da2df 100755
--- a/t/t5324-split-commit-graph.sh
+++ b/t/t5324-split-commit-graph.sh
@@ -210,8 +210,14 @@ test_expect_success 'test merge stragety constants' '
 		git config core.commitGraph true &&
 		test_line_count = 2 $graphdir/commit-graph-chain &&
 		test_commit 15 &&
-		git commit-graph write --reachable --split --size-multiple=10 --expire-time=1980-01-01 &&
+		touch $graphdir/to-delete.graph $graphdir/to-keep.graph &&
+		test-tool chmtime =1546362000 $graphdir/to-delete.graph &&
+		test-tool chmtime =1546362001 $graphdir/to-keep.graph &&
+		git commit-graph write --reachable --split --size-multiple=10 \
+			--expire-time="2019-01-01 12:00 -05:00" &&
 		test_line_count = 1 $graphdir/commit-graph-chain &&
+		test_path_is_missing $graphdir/to-delete.graph &&
+		test_path_is_file $graphdir/to-keep.graph &&
 		ls $graphdir/graph-*.graph >graph-files &&
 		test_line_count = 3 graph-files
 	) &&