diff --git a/temporalio/client.py b/temporalio/client.py
index 822b9ac4..f83d138c 100644
--- a/temporalio/client.py
+++ b/temporalio/client.py
@@ -6078,11 +6078,24 @@ def on_start(
                         None,
                     )
                     if status and status.code in RPCStatusCode:
-                        err = RPCError(
-                            status.message,
-                            RPCStatusCode(status.code),
-                            err.raw_grpc_status,
-                        )
+                        if (
+                            status.code == RPCStatusCode.ALREADY_EXISTS
+                            and status.details
+                        ):
+                            details = temporalio.api.errordetails.v1.WorkflowExecutionAlreadyStartedFailure()
+                            if status.details[0].Unpack(details):
+                                err = temporalio.exceptions.WorkflowAlreadyStartedError(
+                                    input.start_workflow_input.id,
+                                    input.start_workflow_input.workflow,
+                                    run_id=details.run_id,
+                                )
+                        else:
+                            err = RPCError(
+                                status.message,
+                                RPCStatusCode(status.code),
+                                err.raw_grpc_status,
+                            )
+
                 raise err
         finally:
             if not seen_start:
diff --git a/tests/worker/test_update_with_start.py b/tests/worker/test_update_with_start.py
index 2ab16a93..ff57723d 100644
--- a/tests/worker/test_update_with_start.py
+++ b/tests/worker/test_update_with_start.py
@@ -14,7 +14,6 @@
     Client,
     Interceptor,
     OutboundInterceptor,
-    RPCError,
     StartWorkflowUpdateWithStartInput,
     WithStartWorkflowOperation,
     WorkflowUpdateFailedError,
@@ -24,8 +23,7 @@
 from temporalio.common import (
     WorkflowIDConflictPolicy,
 )
-from temporalio.exceptions import ApplicationError
-from temporalio.service import RPCStatusCode
+from temporalio.exceptions import ApplicationError, WorkflowAlreadyStartedError
 from tests.helpers import (
     new_worker,
 )
@@ -230,15 +228,14 @@ async def _do_execute_update_test(
                     await start_op_2.workflow_handle()
                 ).first_execution_run_id is not None
             else:
-                with pytest.raises(RPCError) as e:
-                    await client.execute_update_with_start_workflow(
+                for aw in [
+                    client.execute_update_with_start_workflow(
                         update_handler, "21", start_workflow_operation=start_op_2
-                    )
-
-                assert e.value.grpc_status.code == RPCStatusCode.ALREADY_EXISTS
-                with pytest.raises(RPCError) as e2:
-                    await start_op_2.workflow_handle()
-                assert e2.value.grpc_status.code == RPCStatusCode.ALREADY_EXISTS
+                    ),
+                    start_op_2.workflow_handle(),
+                ]:
+                    with pytest.raises(WorkflowAlreadyStartedError):
+                        await aw
 
                 assert (
                     await start_op_1.workflow_handle()
@@ -337,18 +334,18 @@ def make_start_op(workflow_id: str):
         # Second UWS start fails because the workflow already exists
         # first execution run ID is not set on the second UWS handle
         start_op_2 = make_start_op("wid-1")
-        with pytest.raises(RPCError) as exc_info:
-            await client.start_update_with_start_workflow(
+
+        for aw in [
+            client.start_update_with_start_workflow(
                 WorkflowForUpdateWithStartTest.my_non_blocking_update,
                 "2",
                 wait_for_stage=WorkflowUpdateStage.COMPLETED,
                 start_workflow_operation=start_op_2,
-            )
-        assert exc_info.value.status == RPCStatusCode.ALREADY_EXISTS
-
-        with pytest.raises(RPCError) as e2:
-            await start_op_2.workflow_handle()
-        assert e2.value.grpc_status.code == RPCStatusCode.ALREADY_EXISTS
+            ),
+            start_op_2.workflow_handle(),
+        ]:
+            with pytest.raises(WorkflowAlreadyStartedError):
+                await aw
 
         # Third UWS start succeeds, but the update fails after acceptance
         start_op_3 = make_start_op("wid-2")
@@ -421,18 +418,18 @@ def make_start_op(workflow_id: str):
         )
 
         start_op_2 = make_start_op(wid)
-        with pytest.raises(RPCError) as exc_info:
-            await client.start_update_with_start_workflow(
+
+        for aw in [
+            client.start_update_with_start_workflow(
                 WorkflowForUpdateWithStartTest.my_non_blocking_update,
                 "2",
                 wait_for_stage=WorkflowUpdateStage.COMPLETED,
                 start_workflow_operation=start_op_2,
-            )
-        assert exc_info.value.grpc_status.code == RPCStatusCode.ALREADY_EXISTS
-
-        with pytest.raises(RPCError) as exc_info2:
-            await start_op_2.workflow_handle()
-        assert exc_info2.value.grpc_status.code == RPCStatusCode.ALREADY_EXISTS
+            ),
+            start_op_2.workflow_handle(),
+        ]:
+            with pytest.raises(WorkflowAlreadyStartedError):
+                await aw
 
 
 async def test_workflow_update_poll_loop(client: Client):