diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 2a94019276..50fb339b8e 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -4301,10 +4301,13 @@ static void enumerate_and_traverse_cruft_objects(struct string_list *fresh_packs
 	/*
 	 * Re-mark only the fresh packs as kept so that objects in
 	 * unknown packs do not halt the reachability traversal early.
+	 * The kept-pack cache was built while those packs were still
+	 * marked, so drop it too.
 	 */
 	repo_for_each_pack(the_repository, p)
 		p->pack_keep_in_core = 0;
 	mark_pack_kept_in_core(fresh_packs, 1);
+	repo_invalidate_kept_pack_caches(the_repository);
 
 	if (prepare_revision_walk(&revs))
 		die(_("revision walk setup failed"));
diff --git a/odb/source-packed.h b/odb/source-packed.h
index a0f6b5096d..c8c6088a69 100644
--- a/odb/source-packed.h
+++ b/odb/source-packed.h
@@ -25,7 +25,8 @@ struct odb_source_packed {
 	 * Should not be accessed directly, but via
 	 * `packfile_store_get_kept_pack_cache()`. The list of packs gets
 	 * invalidated when the stored flags and the flags passed to
-	 * `packfile_store_get_kept_pack_cache()` mismatch.
+	 * `packfile_store_get_kept_pack_cache()` mismatch, or explicitly via
+	 * `repo_invalidate_kept_pack_caches()`.
 	 */
 	struct {
 		struct packed_git **packs;
diff --git a/packfile.c b/packfile.c
index 4fa5fd67c8..399c0622cd 100644
--- a/packfile.c
+++ b/packfile.c
@@ -1870,6 +1870,22 @@ int packfile_fill_entry(struct packed_git *p,
 	return 1;
 }
 
+static void invalidate_kept_pack_cache(struct odb_source_packed *store)
+{
+	FREE_AND_NULL(store->kept_cache.packs);
+	store->kept_cache.flags = 0;
+}
+
+void repo_invalidate_kept_pack_caches(struct repository *r)
+{
+	struct odb_source *source;
+
+	for (source = r->objects->sources; source; source = source->next) {
+		struct odb_source_files *files = odb_source_files_downcast(source);
+		invalidate_kept_pack_cache(files->packed);
+	}
+}
+
 static void maybe_invalidate_kept_pack_cache(struct odb_source_packed *store,
 					     unsigned flags)
 {
@@ -1877,8 +1893,7 @@ static void maybe_invalidate_kept_pack_cache(struct odb_source_packed *store,
 		return;
 	if (store->kept_cache.flags == flags)
 		return;
-	FREE_AND_NULL(store->kept_cache.packs);
-	store->kept_cache.flags = 0;
+	invalidate_kept_pack_cache(store);
 }
 
 struct packed_git **packfile_store_get_kept_pack_cache(struct odb_source_packed *store,
diff --git a/packfile.h b/packfile.h
index 6d30d15a00..e2db6bfff7 100644
--- a/packfile.h
+++ b/packfile.h
@@ -144,6 +144,13 @@ enum kept_pack_type {
 struct packed_git **packfile_store_get_kept_pack_cache(struct odb_source_packed *store,
 						       unsigned flags);
 
+/*
+ * Drop every packfile store's cache of kept packs, so that the next call
+ * to `packfile_store_get_kept_pack_cache()` rebuilds it, e.g. after
+ * changing which packs are kept in core.
+ */
+void repo_invalidate_kept_pack_caches(struct repository *r);
+
 struct pack_window {
 	struct pack_window *next;
 	unsigned char *base;
diff --git a/t/t5329-pack-objects-cruft.sh b/t/t5329-pack-objects-cruft.sh
index 12cda06373..6302f60b75 100755
--- a/t/t5329-pack-objects-cruft.sh
+++ b/t/t5329-pack-objects-cruft.sh
@@ -332,6 +332,46 @@ test_expect_success 'cruft trees rescue sub-trees, blobs' '
 	)
 '
 
+test_expect_success 'cruft traversal rescues through a pack it was not told about' '
+	git init repo &&
+	test_when_finished "rm -fr repo" &&
+	(
+		cd repo &&
+
+		test_commit packed &&
+		git repack -Ad &&
+		keep="$(basename "$(ls $packdir/pack-*.pack)")" &&
+
+		test_commit old &&
+		test_commit mid &&
+		test_commit new &&
+
+		# "old" has expired, "new" is recent, and "mid" sits in a
+		# pack that pack-objects is not told about. Rescuing "old"
+		# from "new" means walking through that pack.
+		git rev-list --objects --no-object-names packed..old >old &&
+		while read object
+		do
+			test-tool chmtime -1000 \
+				"$objdir/$(test_oid_to_path $object)" || exit 1
+		done <old &&
+		git rev-list --objects --no-object-names old..mid |
+		git pack-objects $packdir/pack >/dev/null &&
+		git prune-packed &&
+
+		cruft="$(echo $keep | git pack-objects --cruft \
+			--cruft-expiration=750.seconds.ago \
+			$packdir/pack)" &&
+		test-tool pack-mtimes "pack-$cruft.mtimes" >actual.raw &&
+
+		cut -d" " -f1 <actual.raw | sort >actual &&
+		git rev-list --objects --no-object-names packed..new >expect.raw &&
+		sort <expect.raw >expect &&
+
+		test_cmp expect actual
+	)
+'
+
 test_expect_success 'expired objects are pruned' '
 	git init repo &&
 	test_when_finished "rm -fr repo" &&