diff --git a/.chronus/changes/bump-pyright-2025-8-18-19-5-32.md b/.chronus/changes/bump-pyright-2025-8-18-19-5-32.md
new file mode 100644
index 00000000000..0f374dce470
--- /dev/null
+++ b/.chronus/changes/bump-pyright-2025-8-18-19-5-32.md
@@ -0,0 +1,7 @@
+---
+changeKind: dependencies
+packages:
+  - "@typespec/http-client-python"
+---
+
+bump pyright version to 1.1.405
\ No newline at end of file
diff --git a/packages/http-client-python/eng/scripts/ci/dev_requirements.txt b/packages/http-client-python/eng/scripts/ci/dev_requirements.txt
index 106a07a8450..1b7a304f9ae 100644
--- a/packages/http-client-python/eng/scripts/ci/dev_requirements.txt
+++ b/packages/http-client-python/eng/scripts/ci/dev_requirements.txt
@@ -1,4 +1,4 @@
-pyright==1.1.391
+pyright==1.1.405
 pylint==3.2.7
 tox==4.16.0
 mypy==1.18.1
diff --git a/packages/http-client-python/generator/pygen/codegen/templates/serialization.py.jinja2 b/packages/http-client-python/generator/pygen/codegen/templates/serialization.py.jinja2
index 6384cd230d9..17699dd39b3 100644
--- a/packages/http-client-python/generator/pygen/codegen/templates/serialization.py.jinja2
+++ b/packages/http-client-python/generator/pygen/codegen/templates/serialization.py.jinja2
@@ -783,7 +783,7 @@ class Serializer:  # pylint: disable=too-many-public-methods
 
             # If dependencies is empty, try with current data class
             # It has to be a subclass of Enum anyway
-            enum_type = self.dependencies.get(data_type, data.__class__)
+            enum_type = self.dependencies.get(data_type, cast(type, data.__class__))
             if issubclass(enum_type, Enum):
                 return Serializer.serialize_enum(data, enum_obj=enum_type)