diff --git a/routemaster/cli.py b/routemaster/cli.py
index 5446d87c..c1c61928 100644
--- a/routemaster/cli.py
+++ b/routemaster/cli.py
@@ -97,7 +97,7 @@ def serve(ctx, bind, debug, workers):  # pragma: no cover
         cron_thread.stop()
 
 
-def _validate_config(app: App):
+def _validate_config(app: App) -> None:
     try:
         validate_config(app, app.config)
     except ValidationError as e:
diff --git a/routemaster/config/model.py b/routemaster/config/model.py
index d1a70a60..37b32cbf 100644
--- a/routemaster/config/model.py
+++ b/routemaster/config/model.py
@@ -160,7 +160,7 @@ class FeedConfig(NamedTuple):
 
 class Webhook(NamedTuple):
     """Configuration for webdook requests."""
-    match: Pattern
+    match: Pattern[str]
     headers: Dict[str, str]
 
 
diff --git a/routemaster/context.py b/routemaster/context.py
index 602c530b..ef1a141a 100644
--- a/routemaster/context.py
+++ b/routemaster/context.py
@@ -1,10 +1,27 @@
 """Context definition for exit condition programs."""
 import datetime
-from typing import Any, Dict, Iterable, Optional, Sequence
+from typing import (
+    TYPE_CHECKING,
+    Any,
+    Dict,
+    Callable,
+    Iterable,
+    Optional,
+    Sequence,
+    ContextManager,
+)
 
-from routemaster.feeds import Feed
 from routemaster.utils import get_path
 
+if TYPE_CHECKING:
+    import requests  # noqa
+    from routemaster.feeds import Feed, FeedResponseLogger  # noqa
+
+FeedLoggingContext = Callable[
+    [str],
+    ContextManager[Callable[['requests.Response'], None]],
+]
+
 
 class Context(object):
     """Execution context for exit condition programs."""
@@ -15,10 +32,10 @@ def __init__(
         label: str,
         metadata: Dict[str, Any],
         now: datetime.datetime,
-        feeds: Dict[str, Feed],
+        feeds: Dict[str, 'Feed'],
         accessed_variables: Iterable[str],
         current_history_entry: Optional[Any],
-        feed_logging_context,
+        feed_logging_context: FeedLoggingContext,
     ) -> None:
         """Create an execution context."""
         if now.tzinfo is None:
@@ -80,8 +97,8 @@ def _pre_warm_feeds(
         self,
         label: str,
         accessed_variables: Iterable[str],
-        logging_context,
-    ):
+        logging_context: FeedLoggingContext,
+    ) -> None:
         for accessed_variable in accessed_variables:
             parts = accessed_variable.split('.')
 
diff --git a/routemaster/cron.py b/routemaster/cron.py
index 855fc3f3..25b409f4 100644
--- a/routemaster/cron.py
+++ b/routemaster/cron.py
@@ -55,7 +55,7 @@ def process_job(
     # Bound when scheduling a specific job for a state
     fn: LabelStateProcessor,
     label_provider: LabelProvider,
-):
+) -> None:
     """Process a single instance of a single cron job."""
 
     def _iter_labels_until_terminating(state_machine, state):
diff --git a/routemaster/feeds.py b/routemaster/feeds.py
index d8dc2bf1..797716de 100644
--- a/routemaster/feeds.py
+++ b/routemaster/feeds.py
@@ -6,9 +6,12 @@
 from dataclasses import InitVar, dataclass
 
 from routemaster.utils import get_path, template_url
+from routemaster.config import StateMachine
 
+FeedResponseLogger = Callable[[requests.Response], None]
 
-def feeds_for_state_machine(state_machine) -> Dict[str, 'Feed']:
+
+def feeds_for_state_machine(state_machine: StateMachine) -> Dict[str, 'Feed']:
     """Get a mapping of feed prefixes to unfetched feeds."""
     return {
         x.name: Feed(x.url, state_machine.name)  # type: ignore
@@ -42,7 +45,7 @@ class Feed:
     def prefetch(
         self,
         label: str,
-        log_response: Callable[[requests.Response], None] = lambda x: None,
+        log_response: FeedResponseLogger = lambda x: None,
     ) -> None:
         """Trigger the fetching of a feed's data."""
         if self.data is not None:
diff --git a/routemaster/logging/base.py b/routemaster/logging/base.py
index d474c355..c5b82f56 100644
--- a/routemaster/logging/base.py
+++ b/routemaster/logging/base.py
@@ -1,12 +1,13 @@
 """Base class for logging plugins."""
 
 import contextlib
+from typing import Any
 
 
 class BaseLogger:
     """Base class for logging plugins."""
 
-    def __init__(self, config, *args, **kwargs) -> None:
+    def __init__(self, config: Any, **kwargs: str) -> None:
         self.config = config
 
     def init_flask(self, flask_app):
diff --git a/routemaster/logging/plugins.py b/routemaster/logging/plugins.py
index 76afc62e..20aa68a5 100644
--- a/routemaster/logging/plugins.py
+++ b/routemaster/logging/plugins.py
@@ -1,5 +1,6 @@
 """Plugin loading and configuration."""
 import importlib
+from typing import List
 
 from routemaster.config import Config, LoggingPluginConfig
 from routemaster.logging.base import BaseLogger
@@ -9,7 +10,7 @@ class PluginConfigurationException(Exception):
     """Raised to signal an invalid plugin that was loaded."""
 
 
-def register_loggers(config: Config):
+def register_loggers(config: Config) -> List[BaseLogger]:
     """
     Iterate through all plugins in the config file and instatiate them.
     """
diff --git a/routemaster/logging/python_logger.py b/routemaster/logging/python_logger.py
index ad658385..abdb3f75 100644
--- a/routemaster/logging/python_logger.py
+++ b/routemaster/logging/python_logger.py
@@ -3,15 +3,19 @@
 import time
 import logging
 import contextlib
+from typing import TYPE_CHECKING
 
 from routemaster.logging.base import BaseLogger
 
+if TYPE_CHECKING:
+    from routemaster.config import Config  # noqa
+
 
 class PythonLogger(BaseLogger):
     """Routemaster logging interface for Python's logging library."""
 
-    def __init__(self, *args, log_level: str) -> None:
-        super().__init__(*args)
+    def __init__(self, config: 'Config', log_level: str) -> None:
+        super().__init__(config)
 
         logging.basicConfig(
             format=(
diff --git a/routemaster/logging/split_logger.py b/routemaster/logging/split_logger.py
index 8021619c..9c83f694 100644
--- a/routemaster/logging/split_logger.py
+++ b/routemaster/logging/split_logger.py
@@ -2,16 +2,19 @@
 
 import functools
 import contextlib
-from typing import List
+from typing import TYPE_CHECKING, List
 
 from routemaster.logging.base import BaseLogger
 
+if TYPE_CHECKING:
+    from routemaster.config import Config  # noqa
+
 
 class SplitLogger(BaseLogger):
     """Proxies logging calls to all loggers in a list."""
 
-    def __init__(self, *args, loggers: List[BaseLogger]) -> None:
-        super().__init__(*args)
+    def __init__(self, config: 'Config', loggers: List[BaseLogger]) -> None:
+        super().__init__(config)
 
         self.loggers = loggers
 
diff --git a/routemaster/logging/tests/test_loggers.py b/routemaster/logging/tests/test_loggers.py
index 7933c71c..c5adc0dc 100644
--- a/routemaster/logging/tests/test_loggers.py
+++ b/routemaster/logging/tests/test_loggers.py
@@ -18,7 +18,7 @@
     ]}),
     (SplitLogger, {'loggers': [
         PythonLogger(None, log_level='WARN'),
-        BaseLogger(None, {}),
+        BaseLogger(None),
     ]}),
 ]
 
diff --git a/routemaster/middleware.py b/routemaster/middleware.py
index b2efef49..a65f3435 100644
--- a/routemaster/middleware.py
+++ b/routemaster/middleware.py
@@ -11,7 +11,7 @@
 ACTIVE_MIDDLEWARES = []
 
 
-def middleware(fn: WSGIMiddleware):
+def middleware(fn: WSGIMiddleware) -> WSGIMiddleware:
     """Decorator: add `fn` to ACTIVE_MIDDLEWARES."""
     ACTIVE_MIDDLEWARES.append(fn)
     return fn
diff --git a/routemaster/state_machine/actions.py b/routemaster/state_machine/actions.py
index 01add392..858ca7c2 100644
--- a/routemaster/state_machine/actions.py
+++ b/routemaster/state_machine/actions.py
@@ -98,7 +98,10 @@ def process_action(
     return True
 
 
-def _calculate_idempotency_token(label: LabelRef, latest_history) -> str:
+def _calculate_idempotency_token(
+    label: LabelRef,
+    latest_history: History,
+) -> str:
     """
     We want to make sure that an action is only performed once.
 
diff --git a/routemaster/state_machine/api.py b/routemaster/state_machine/api.py
index 258439b2..9e3feea6 100644
--- a/routemaster/state_machine/api.py
+++ b/routemaster/state_machine/api.py
@@ -151,7 +151,7 @@ def _process_transitions_for_metadata_update(
     label: LabelRef,
     state_machine: StateMachine,
     state_pending_update: State,
-):
+) -> None:
     with app.session.begin_nested():
         lock_label(app, label)
         current_state = get_current_state(app, label, state_machine)
@@ -223,7 +223,7 @@ def process_cron(
     app: App,
     state_machine: StateMachine,
     state: State,
-):
+) -> None:
     """
     Cron event entrypoint.
     """
diff --git a/routemaster/tests/test_layering.py b/routemaster/tests/test_layering.py
index 01d10e70..c99b0e51 100644
--- a/routemaster/tests/test_layering.py
+++ b/routemaster/tests/test_layering.py
@@ -27,7 +27,6 @@
     ('exit_conditions', 'utils'),
 
     ('context', 'utils'),
-    ('context', 'feeds'),
 
     ('config', 'exit_conditions'),
     ('config', 'context'),
@@ -57,6 +56,7 @@
     ('state_machine', 'webhooks'),
 
     ('feeds', 'utils'),
+    ('feeds', 'config'),
 
     ('webhooks', 'config'),
 
@@ -135,10 +135,34 @@ def test_layers():
         code = compile(contents, module_name, 'exec')
 
         last_import_source = None
+        last_load_name = None
+        skip_to_offset = None
 
-        top_level_import = False
+        for offset, instruction in enumerate(dis.get_instructions(code)):
+
+            # Skip over checking code that is within a block like this:
+            #     if TYPE_CHECKING:
+            #         import...
+            if skip_to_offset == offset:
+                skip_to_offset = None
+            elif skip_to_offset is not None:
+                continue
+
+            if instruction.opname == 'LOAD_NAME':
+                last_load_name = instruction.argval
+                continue
+
+            elif (
+                instruction.opname == 'POP_JUMP_IF_FALSE' and
+                last_load_name == 'TYPE_CHECKING'
+            ):
+                skip_to_offset = instruction.argval
+                continue
+
+            last_load_name = None
+
+            # Now do the actual import checking
 
-        for instruction in dis.get_instructions(code):
             if instruction.opname == 'IMPORT_NAME':
                 import_target = instruction.argval
 
diff --git a/routemaster/validation.py b/routemaster/validation.py
index 379be7ad..2fd92958 100644
--- a/routemaster/validation.py
+++ b/routemaster/validation.py
@@ -14,13 +14,13 @@ class ValidationError(Exception):
     pass
 
 
-def validate_config(app: App, config: Config):
+def validate_config(app: App, config: Config) -> None:
     """Validate that a given config satisfies invariants."""
     for state_machine in config.state_machines.values():
         _validate_state_machine(app, state_machine)
 
 
-def _validate_state_machine(app: App, state_machine: StateMachine):
+def _validate_state_machine(app: App, state_machine: StateMachine) -> None:
     """Validate that a given state machine is internally consistent."""
     with app.new_session():
         _validate_route_start_to_end(state_machine)
diff --git a/setup.cfg b/setup.cfg
index 82beb800..ab08bdc3 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -9,6 +9,8 @@ no-accept-encodings=true
 [mypy]
 ignore_missing_imports=true
 strict_optional=true
+disallow_any_generics=true
+disallow_incomplete_defs=true
 
 [coverage:run]
 branch=True