diff --git a/docs/source/developer_guide/guides/3_simple_cpp_stage.md b/docs/source/developer_guide/guides/3_simple_cpp_stage.md
index 610fe49f8d..b9362e9755 100644
--- a/docs/source/developer_guide/guides/3_simple_cpp_stage.md
+++ b/docs/source/developer_guide/guides/3_simple_cpp_stage.md
@@ -383,7 +383,7 @@ As mentioned in the previous section, our `_build_single` method needs to be upd
 
 ```python
 def _build_single(self, builder: mrc.Builder, input_node: mrc.SegmentObject) -> mrc.SegmentObject:
-    if self._build_cpp_node() and isinstance(self._input_type, ControlMessage):
+    if self._build_cpp_node() and issubclass(self._input_type, ControlMessage):
         from ._lib import pass_thru_cpp
 
         node = pass_thru_cpp.PassThruStage(builder, self.unique_name)
@@ -438,7 +438,7 @@ class PassThruStage(PassThruTypeMixin, GpuAndCpuMixin, SinglePortStage):
         return message
 
     def _build_single(self, builder: mrc.Builder, input_node: mrc.SegmentObject) -> mrc.SegmentObject:
-        if self._build_cpp_node() and isinstance(self._input_type, ControlMessage):
+        if self._build_cpp_node() and issubclass(self._input_type, ControlMessage):
             from ._lib import pass_thru_cpp
 
             node = pass_thru_cpp.PassThruStage(builder, self.unique_name)
diff --git a/examples/developer_guide/3_simple_cpp_stage/src/simple_cpp_stage/pass_thru.py b/examples/developer_guide/3_simple_cpp_stage/src/simple_cpp_stage/pass_thru.py
index 8364b89644..728e8ef431 100644
--- a/examples/developer_guide/3_simple_cpp_stage/src/simple_cpp_stage/pass_thru.py
+++ b/examples/developer_guide/3_simple_cpp_stage/src/simple_cpp_stage/pass_thru.py
@@ -53,9 +53,8 @@ def on_data(self, message: typing.Any):
         return message
 
     def _build_single(self, builder: mrc.Builder, input_node: mrc.SegmentObject) -> mrc.SegmentObject:
-        if self._build_cpp_node() and isinstance(self._input_type, ControlMessage):
+        if self._build_cpp_node() and issubclass(self._input_type, ControlMessage):
             from ._lib import pass_thru_cpp
-
             node = pass_thru_cpp.PassThruStage(builder, self.unique_name)
         else:
             node = builder.make_node(self.unique_name, ops.map(self.on_data))