diff --git a/lib/galaxy_test/api/test_workflows.py b/lib/galaxy_test/api/test_workflows.py
index 7a6589afd2e..f1e1c9fe4e9 100644
--- a/lib/galaxy_test/api/test_workflows.py
+++ b/lib/galaxy_test/api/test_workflows.py
@@ -6538,7 +6538,7 @@ steps:
                 "parameters_normalized": True,
                 "parameters": dumps(parameters),
             }
-            invocation_response = self._post(f"workflows/{workflow_id}/usage", data=workflow_request)
+            invocation_response = self._post(f"workflows/{workflow_id}/usage", data=workflow_request, json=True)
             self._assert_status_code_is(invocation_response, 200)
             time.sleep(5)
             self.dataset_populator.wait_for_history(history_id, assert_ok=True)
@@ -6590,7 +6590,7 @@ steps:
                 "parameters_normalized": True,
                 "parameters": dumps(parameters),
             }
-            invocation_response = self._post(f"workflows/{workflow_id}/usage", data=workflow_request)
+            invocation_response = self._post(f"workflows/{workflow_id}/usage", data=workflow_request, json=True)
             self._assert_status_code_is(invocation_response, 200)
             time.sleep(5)
             self.dataset_populator.wait_for_history(history_id, assert_ok=True)