diff --git a/caimira/apps/calculator/__init__.py b/caimira/apps/calculator/__init__.py
index 4072648c..513187e1 100644
--- a/caimira/apps/calculator/__init__.py
+++ b/caimira/apps/calculator/__init__.py
@@ -92,7 +92,7 @@ class Missing404Handler(BaseRequestHandler):
 
 
 class ConcentrationModel(BaseRequestHandler):
-    async def post(self):
+    async def post(self) -> None:
         requested_model_config = {
             name: self.get_argument(name) for name in self.request.arguments
         }
@@ -137,7 +137,7 @@ class ConcentrationModelJsonResponse(BaseRequestHandler):
         """
         pass
 
-    async def post(self):
+    async def post(self) -> None:
         """
         Expects algorithm input in HTTP POST request body in JSON format.
         Returns report data (algorithm output) in HTTP POST response body in JSON format.
@@ -168,7 +168,7 @@ class ConcentrationModelJsonResponse(BaseRequestHandler):
 
 
 class StaticModel(BaseRequestHandler):
-    async def get(self):
+    async def get(self) -> None:
         form = model_generator.FormData.from_dict(model_generator.baseline_raw_form_data())
         base_url = self.request.protocol + "://" + self.request.host
         report_generator: ReportGenerator = self.settings['report_generator']
diff --git a/caimira/apps/expert.py b/caimira/apps/expert.py
index 361dc1c4..6d489697 100644
--- a/caimira/apps/expert.py
+++ b/caimira/apps/expert.py
@@ -901,7 +901,7 @@ class CAIMIRAStateBuilder(state.StateBuilder):
 
 
 class ExpertApplication(Controller):
-    def __init__(self):
+    def __init__(self) -> None:
         self._debug_output = widgets.Output()
 
         #: A list of scenario name and ModelState instances. This is intended to be
diff --git a/caimira/state.py b/caimira/state.py
index d65fe2c5..b990e7cf 100644
--- a/caimira/state.py
+++ b/caimira/state.py
@@ -53,7 +53,7 @@ class DataclassState(typing.Generic[Datamodel_T]):
         yield
         object.__setattr__(self, '_use_base_setattr', False)
 
-    def dcs_instance(self) -> Datamodel_T:
+    def dcs_instance(self) -> typing.Union[None, Datamodel_T]:
         """
         Return the instance that this state represents. The instance returned
         is immutable, so it is advised to call this method each time that
diff --git a/caimira/tests/apps/calculator/test_report_generator.py b/caimira/tests/apps/calculator/test_report_generator.py
index 4dcba65c..18190777 100644
--- a/caimira/tests/apps/calculator/test_report_generator.py
+++ b/caimira/tests/apps/calculator/test_report_generator.py
@@ -11,7 +11,7 @@ from caimira.apps.calculator.report_generator import ReportGenerator, readable_m
 import caimira.apps.calculator.report_generator as rep_gen
 
 
-def test_generate_report(baseline_form):
+def test_generate_report(baseline_form) -> None:
     # This is a simple test that confirms that given a model, we can actually
     # generate a report for it. Because this is what happens in the caimira
     # calculator, we confirm that the generation happens within a reasonable