diff --git a/temporalio/lib/temporalio/internal/client/implementation.rb b/temporalio/lib/temporalio/internal/client/implementation.rb
index 59cb9f6c..dcc0ae08 100644
--- a/temporalio/lib/temporalio/internal/client/implementation.rb
+++ b/temporalio/lib/temporalio/internal/client/implementation.rb
@@ -228,7 +228,7 @@ def start_update_with_start_workflow(input)
                 if details
                   e = Error::WorkflowAlreadyStartedError.new(
                     workflow_id: start_options.id,
-                    workflow_type: start_req.workflow_type,
+                    workflow_type: start_req.workflow_type.name,
                     run_id: details.run_id
                   )
                 end
diff --git a/temporalio/test/worker_workflow_handler_test.rb b/temporalio/test/worker_workflow_handler_test.rb
index 4e3fd48a..c4ab8880 100644
--- a/temporalio/test/worker_workflow_handler_test.rb
+++ b/temporalio/test/worker_workflow_handler_test.rb
@@ -742,14 +742,16 @@ def test_update_with_start_simple
         UpdateWithStartWorkflow, 123,
         id:, task_queue: worker.task_queue, id_conflict_policy: Temporalio::WorkflowIDConflictPolicy::FAIL
       )
-      assert_raises(Temporalio::Error::WorkflowAlreadyStartedError) do
+      err = assert_raises(Temporalio::Error::WorkflowAlreadyStartedError) do
         env.client.execute_update_with_start_workflow(
           UpdateWithStartWorkflow.increment_counter, 456, start_workflow_operation:
         )
       end
-      assert_raises(Temporalio::Error::WorkflowAlreadyStartedError) do
+      assert_equal 'UpdateWithStartWorkflow', err.workflow_type
+      err = assert_raises(Temporalio::Error::WorkflowAlreadyStartedError) do
         start_workflow_operation.workflow_handle
       end
+      assert_equal 'UpdateWithStartWorkflow', err.workflow_type
     end
   end
 
@@ -830,15 +832,17 @@ def test_update_with_start_start_fail
         UpdateWithStartWorkflow, 123,
         id:, task_queue: worker.task_queue, id_conflict_policy: Temporalio::WorkflowIDConflictPolicy::FAIL
       )
-      assert_raises(Temporalio::Error::WorkflowAlreadyStartedError) do
+      err = assert_raises(Temporalio::Error::WorkflowAlreadyStartedError) do
         env.client.start_update_with_start_workflow(
           UpdateWithStartWorkflow.increment_counter, 456,
           wait_for_stage: Temporalio::Client::WorkflowUpdateWaitStage::ACCEPTED, start_workflow_operation:
         )
       end
-      assert_raises(Temporalio::Error::WorkflowAlreadyStartedError) do
+      assert_equal 'UpdateWithStartWorkflow', err.workflow_type
+      err = assert_raises(Temporalio::Error::WorkflowAlreadyStartedError) do
         start_workflow_operation.workflow_handle
       end
+      assert_equal 'UpdateWithStartWorkflow', err.workflow_type
     end
   end