diff --git a/core/src/apps/debug/__init__.py b/core/src/apps/debug/__init__.py
index 74b22600ec..e3cee6bf3c 100644
--- a/core/src/apps/debug/__init__.py
+++ b/core/src/apps/debug/__init__.py
@@ -166,7 +166,7 @@ if __debug__:
 
         wire.add(MessageType.LoadDevice, __name__, "load_device")
         wire.add(MessageType.DebugLinkShowText, __name__, "show_text")
-        wire.register(MessageType.DebugLinkDecision, dispatch_DebugLinkDecision)
+        wire.register(MessageType.DebugLinkDecision, dispatch_DebugLinkDecision)  # type: ignore
         wire.register(MessageType.DebugLinkGetState, dispatch_DebugLinkGetState)
         wire.register(MessageType.DebugLinkReseedRandom, dispatch_DebugLinkReseedRandom)
         wire.register(MessageType.DebugLinkRecordScreen, dispatch_DebugLinkRecordScreen)
diff --git a/core/src/trezor/wire/__init__.py b/core/src/trezor/wire/__init__.py
index e09ac7ead5..51d69328f4 100644
--- a/core/src/trezor/wire/__init__.py
+++ b/core/src/trezor/wire/__init__.py
@@ -51,15 +51,19 @@ if False:
         Any,
         Awaitable,
         Callable,
+        Coroutine,
         Dict,
         Iterable,
         Optional,
         Tuple,
         Type,
+        TypeVar,
     )
     from trezorio import WireInterface
 
-    Handler = Callable[..., loop.Task]
+    Msg = TypeVar("Msg", bound=protobuf.MessageType)
+    HandlerTask = Coroutine[Any, Any, protobuf.MessageType]
+    Handler = Callable[["Context", Msg], HandlerTask]
 
 
 # Maps a wire type directly to a handler.
@@ -257,7 +261,7 @@ class UnexpectedMessageError(Exception):
 async def handle_session(iface: WireInterface, session_id: int) -> None:
     ctx = Context(iface, session_id)
     next_reader = None  # type: Optional[codec_v1.Reader]
-    res_msg = None
+    res_msg = None  # type: Optional[protobuf.MessageType]
     req_reader = None
     req_type = None
     req_msg = None
@@ -301,7 +305,7 @@ async def handle_session(iface: WireInterface, session_id: int) -> None:
 
             # We need to find a handler for this message type.  Should not
             # raise.
-            handler = get_workflow_handler(req_reader)
+            handler = find_handler(iface, req_reader.type)
 
             if handler is None:
                 # If no handler is found, we can skip decoding and directly
@@ -314,7 +318,7 @@ async def handle_session(iface: WireInterface, session_id: int) -> None:
                 # We found a valid handler for this message type.
 
                 # Workflow task, declared for the `workflow.on_close` call later.
-                wf_task = None  # type: Optional[loop.Task]
+                wf_task = None  # type: Optional[HandlerTask]
 
                 # Here we make sure we always respond with a Failure response
                 # in case of any errors.
@@ -407,9 +411,9 @@ async def handle_session(iface: WireInterface, session_id: int) -> None:
                 log.exception(__name__, exc)
 
 
-def get_workflow_handler(reader: codec_v1.Reader) -> Optional[Handler]:
-    msg_type = reader.type
-
+def find_registered_workflow_handler(
+    iface: WireInterface, msg_type: int
+) -> Optional[Handler]:
     if msg_type in workflow_handlers:
         # Message has a handler available, return it directly.
         handler = workflow_handlers[msg_type]
@@ -426,6 +430,9 @@ def get_workflow_handler(reader: codec_v1.Reader) -> Optional[Handler]:
     return handler
 
 
+find_handler = find_registered_workflow_handler
+
+
 def import_workflow(pkgname: str, modname: str) -> Any:
     modpath = "%s.%s" % (pkgname, modname)
     module = __import__(modpath, None, None, (modname,), 0)