diff --git a/builtin/commit-graph.c b/builtin/commit-graph.c
index 4247fbde95..51c4040ea6 100644
--- a/builtin/commit-graph.c
+++ b/builtin/commit-graph.c
@@ -192,7 +192,7 @@ static int git_commit_graph_write_config(const char *var, const char *value,
 
 static int graph_write(int argc, const char **argv)
 {
-	struct string_list pack_indexes = STRING_LIST_INIT_NODUP;
+	struct string_list pack_indexes = STRING_LIST_INIT_DUP;
 	struct strbuf buf = STRBUF_INIT;
 	struct oidset commits = OIDSET_INIT;
 	struct object_directory *odb = NULL;
@@ -273,8 +273,8 @@ static int graph_write(int argc, const char **argv)
 
 	if (opts.stdin_packs) {
 		while (strbuf_getline(&buf, stdin) != EOF)
-			string_list_append(&pack_indexes,
-					   strbuf_detach(&buf, NULL));
+			string_list_append_nodup(&pack_indexes,
+						 strbuf_detach(&buf, NULL));
 	} else if (opts.stdin_commits) {
 		oidset_init(&commits, 0);
 		if (opts.progress)
diff --git a/commit-graph.c b/commit-graph.c
index 265c010122..d0c94600ba 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -1679,7 +1679,7 @@ int write_commit_graph_reachable(struct object_directory *odb,
 }
 
 static int fill_oids_from_packs(struct write_commit_graph_context *ctx,
-				struct string_list *pack_indexes)
+				const struct string_list *pack_indexes)
 {
 	uint32_t i;
 	struct strbuf progress_title = STRBUF_INIT;
@@ -2259,7 +2259,7 @@ out:
 }
 
 int write_commit_graph(struct object_directory *odb,
-		       struct string_list *pack_indexes,
+		       const struct string_list *const pack_indexes,
 		       struct oidset *commits,
 		       enum commit_graph_write_flags flags,
 		       const struct commit_graph_opts *opts)
diff --git a/commit-graph.h b/commit-graph.h
index 04a94e1830..2e3ac35237 100644
--- a/commit-graph.h
+++ b/commit-graph.h
@@ -142,7 +142,7 @@ int write_commit_graph_reachable(struct object_directory *odb,
 				 enum commit_graph_write_flags flags,
 				 const struct commit_graph_opts *opts);
 int write_commit_graph(struct object_directory *odb,
-		       struct string_list *pack_indexes,
+		       const struct string_list *pack_indexes,
 		       struct oidset *commits,
 		       enum commit_graph_write_flags flags,
 		       const struct commit_graph_opts *opts);