diff --git a/tools/test-case-generators/generate-all-test-cases b/tools/test-case-generators/generate-all-test-cases
index 7337a67f1..27f92e743 100755
--- a/tools/test-case-generators/generate-all-test-cases
+++ b/tools/test-case-generators/generate-all-test-cases
@@ -1354,8 +1354,8 @@ def get_args():
         "--output",
         metavar="DIR",
         type=os.path.abspath,
-        help="directory for storing generated image test cases",
-        required=True
+        default="test/data/manifests",
+        help="directory for storing generated image test cases (default 'test/data/manifests')"
     )
     parser.add_argument(
         "--sources",