diff --git a/swh/storage/cassandra/storage.py b/swh/storage/cassandra/storage.py
--- a/swh/storage/cassandra/storage.py
+++ b/swh/storage/cassandra/storage.py
@@ -56,7 +56,7 @@
         self.journal_writer = JournalWriter(journal_writer)
         self.objstorage = ObjStorage(objstorage)
 
-    def check_config(self, *, check_write):
+    def check_config(self, *, check_write: bool) -> bool:
         self._cql_runner.check_read()
 
         return True
diff --git a/swh/storage/in_memory.py b/swh/storage/in_memory.py
--- a/swh/storage/in_memory.py
+++ b/swh/storage/in_memory.py
@@ -175,7 +175,7 @@
 
         self.objstorage = ObjStorage({"cls": "memory", "args": {}})
 
-    def check_config(self, *, check_write):
+    def check_config(self, *, check_write: bool) -> bool:
         return True
 
     def _content_add(self, contents: List[Content], with_data: bool) -> Dict:
diff --git a/swh/storage/interface.py b/swh/storage/interface.py
--- a/swh/storage/interface.py
+++ b/swh/storage/interface.py
@@ -53,7 +53,7 @@
 
 class StorageInterface:
     @remote_api_endpoint("check_config")
-    def check_config(self, *, check_write):
+    def check_config(self, *, check_write: bool) -> bool:
         """Check that the storage is configured and ready to go."""
         ...
 
diff --git a/swh/storage/storage.py b/swh/storage/storage.py
--- a/swh/storage/storage.py
+++ b/swh/storage/storage.py
@@ -144,7 +144,7 @@
 
     @timed
     @db_transaction()
-    def check_config(self, *, check_write, db=None, cur=None):
+    def check_config(self, *, check_write: bool, db=None, cur=None) -> bool:
 
         if not self.objstorage.check_config(check_write=check_write):
             return False