diff --git a/signalbot/api.py b/signalbot/api.py
index c78577b..c5a6df9 100644
--- a/signalbot/api.py
+++ b/signalbot/api.py
@@ -128,7 +128,7 @@ async def stop_typing(self, receiver: str):
         ):
             raise StopTypingError
 
-    async def get_groups(self):
+    async def get_groups(self) -> list[dict[str, Any]]:
         uri = self._groups_uri()
         try:
             async with aiohttp.ClientSession() as session:
diff --git a/signalbot/bot.py b/signalbot/bot.py
index a553625..5aeed3e 100644
--- a/signalbot/bot.py
+++ b/signalbot/bot.py
@@ -258,9 +258,9 @@ async def _detect_groups(self):
         # reset group lookups to avoid stale data
         self.groups = await self._signal.get_groups()
 
-        self._groups_by_id = {}
-        self._groups_by_internal_id = {}
-        self._groups_by_name = defaultdict(list)
+        self._groups_by_id: dict[str, dict[str, Any]] = {}
+        self._groups_by_internal_id: dict[str, dict[str, Any]] = {}
+        self._groups_by_name: defaultdict[str, list[dict[str, Any]]] = defaultdict(list)
         for group in self.groups:
             self._groups_by_id[group["id"]] = group
             self._groups_by_internal_id[group["internal_id"]] = group