diff --git a/sha1_file.c b/sha1_file.c
index 725de7f9cfa..a41cc4f65fe 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -3406,9 +3406,16 @@ static int loose_from_alt_odb(struct alternate_object_database *alt,
 			      void *vdata)
 {
 	struct loose_alt_odb_data *data = vdata;
-	return for_each_loose_file_in_objdir(alt->base,
-					     data->cb, NULL, NULL,
-					     data->data);
+	struct strbuf buf = STRBUF_INIT;
+	int r;
+
+	/* copy base not including trailing '/' */
+	strbuf_add(&buf, alt->base, alt->name - alt->base - 1);
+	r = for_each_loose_file_in_objdir_buf(&buf,
+					      data->cb, NULL, NULL,
+					      data->data);
+	strbuf_release(&buf);
+	return r;
 }
 
 int for_each_loose_object(each_loose_object_fn cb, void *data)
diff --git a/t/t5304-prune.sh b/t/t5304-prune.sh
index e32e46dee10..0794d33dad6 100755
--- a/t/t5304-prune.sh
+++ b/t/t5304-prune.sh
@@ -253,4 +253,12 @@ test_expect_success 'prune .git/shallow' '
 	test_path_is_missing .git/shallow
 '
 
+test_expect_success 'prune: handle alternate object database' '
+	test_create_repo A &&
+	git -C A commit --allow-empty -m "initial commit" &&
+	git clone --shared A B &&
+	git -C B commit --allow-empty -m "next commit" &&
+	git -C B prune
+'
+
 test_done