diff --git a/packfile.c b/packfile.c
index fc2d7c2190..2023df1b75 100644
--- a/packfile.c
+++ b/packfile.c
@@ -1010,6 +1010,16 @@ void reprepare_packed_git(struct repository *r)
 	struct object_directory *odb;
 
 	obj_read_lock();
+
+	/*
+	 * Reprepare alt odbs, in case the alternates file was modified
+	 * during the course of this process. This only _adds_ odbs to
+	 * the linked list, so existing odbs will continue to exist for
+	 * the lifetime of the process.
+	 */
+	r->objects->loaded_alternates = 0;
+	prepare_alt_odb(r);
+
 	for (odb = r->objects->odb; odb; odb = odb->next)
 		odb_clear_loose_cache(odb);