diff --git a/durabletask/internal/proto_task_hub_sidecar_service_stub.py b/durabletask/internal/proto_task_hub_sidecar_service_stub.py
new file mode 100644
index 0000000..f91a15c
--- /dev/null
+++ b/durabletask/internal/proto_task_hub_sidecar_service_stub.py
@@ -0,0 +1,34 @@
+from typing import Any, Callable, Protocol
+
+
+class ProtoTaskHubSidecarServiceStub(Protocol):
+    """A stub class roughly matching the TaskHubSidecarServiceStub generated from the .proto file.
+    Used by Azure Functions during orchestration and entity executions to inject custom behavior,
+    as no real sidecar stub is available.
+    """
+    Hello: Callable[..., Any]
+    StartInstance: Callable[..., Any]
+    GetInstance: Callable[..., Any]
+    RewindInstance: Callable[..., Any]
+    WaitForInstanceStart: Callable[..., Any]
+    WaitForInstanceCompletion: Callable[..., Any]
+    RaiseEvent: Callable[..., Any]
+    TerminateInstance: Callable[..., Any]
+    SuspendInstance: Callable[..., Any]
+    ResumeInstance: Callable[..., Any]
+    QueryInstances: Callable[..., Any]
+    PurgeInstances: Callable[..., Any]
+    GetWorkItems: Callable[..., Any]
+    CompleteActivityTask: Callable[..., Any]
+    CompleteOrchestratorTask: Callable[..., Any]
+    CompleteEntityTask: Callable[..., Any]
+    StreamInstanceHistory: Callable[..., Any]
+    CreateTaskHub: Callable[..., Any]
+    DeleteTaskHub: Callable[..., Any]
+    SignalEntity: Callable[..., Any]
+    GetEntity: Callable[..., Any]
+    QueryEntities: Callable[..., Any]
+    CleanEntityStorage: Callable[..., Any]
+    AbandonTaskActivityWorkItem: Callable[..., Any]
+    AbandonTaskOrchestratorWorkItem: Callable[..., Any]
+    AbandonTaskEntityWorkItem: Callable[..., Any]
diff --git a/durabletask/worker.py b/durabletask/worker.py
index fae345c..5e95ca8 100644
--- a/durabletask/worker.py
+++ b/durabletask/worker.py
@@ -23,6 +23,7 @@
 from durabletask.internal.helpers import new_timestamp
 from durabletask.entities import DurableEntity, EntityLock, EntityInstanceId, EntityContext
 from durabletask.internal.orchestration_entity_context import OrchestrationEntityContext
+from durabletask.internal.proto_task_hub_sidecar_service_stub import ProtoTaskHubSidecarServiceStub
 import durabletask.internal.helpers as ph
 import durabletask.internal.exceptions as pe
 import durabletask.internal.orchestrator_service_pb2 as pb
@@ -629,7 +630,7 @@ def stop(self):
     def _execute_orchestrator(
             self,
             req: pb.OrchestratorRequest,
-            stub: stubs.TaskHubSidecarServiceStub,
+            stub: Union[stubs.TaskHubSidecarServiceStub, ProtoTaskHubSidecarServiceStub],
             completionToken,
     ):
         try:
@@ -677,7 +678,7 @@ def _execute_orchestrator(
     def _cancel_orchestrator(
             self,
             req: pb.OrchestratorRequest,
-            stub: stubs.TaskHubSidecarServiceStub,
+            stub: Union[stubs.TaskHubSidecarServiceStub, ProtoTaskHubSidecarServiceStub],
             completionToken,
     ):
         stub.AbandonTaskOrchestratorWorkItem(
@@ -690,7 +691,7 @@ def _cancel_orchestrator(
     def _execute_activity(
             self,
             req: pb.ActivityRequest,
-            stub: stubs.TaskHubSidecarServiceStub,
+            stub: Union[stubs.TaskHubSidecarServiceStub, ProtoTaskHubSidecarServiceStub],
             completionToken,
     ):
         instance_id = req.orchestrationInstance.instanceId
@@ -723,7 +724,7 @@ def _execute_activity(
     def _cancel_activity(
             self,
             req: pb.ActivityRequest,
-            stub: stubs.TaskHubSidecarServiceStub,
+            stub: Union[stubs.TaskHubSidecarServiceStub, ProtoTaskHubSidecarServiceStub],
             completionToken,
     ):
         stub.AbandonTaskActivityWorkItem(
@@ -736,7 +737,7 @@ def _cancel_activity(
     def _execute_entity_batch(
             self,
             req: Union[pb.EntityBatchRequest, pb.EntityRequest],
-            stub: stubs.TaskHubSidecarServiceStub,
+            stub: Union[stubs.TaskHubSidecarServiceStub, ProtoTaskHubSidecarServiceStub],
             completionToken,
     ):
         if isinstance(req, pb.EntityRequest):
@@ -804,7 +805,7 @@ def _execute_entity_batch(
     def _cancel_entity_batch(
             self,
             req: Union[pb.EntityBatchRequest, pb.EntityRequest],
-            stub: stubs.TaskHubSidecarServiceStub,
+            stub: Union[stubs.TaskHubSidecarServiceStub, ProtoTaskHubSidecarServiceStub],
             completionToken,
     ):
         stub.AbandonTaskEntityWorkItem(