diff --git a/tests/onnx/test_onnx_graph_transformations.py b/tests/onnx/test_onnx_graph_transformations.py
index bed539eaccb..c06ac5af971 100644
--- a/tests/onnx/test_onnx_graph_transformations.py
+++ b/tests/onnx/test_onnx_graph_transformations.py
@@ -85,6 +85,7 @@ def test_merge_decoders(self, *args):
                 tmpdir,
                 task=task,
                 no_post_process=True,
+                legacy=True,
             )
 
             decoder = onnx.load(os.path.join(tmpdir, "decoder_model.onnx"))