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
@@ -558,7 +558,7 @@
 
         return {"release:add": len(to_add)}
 
-    def release_missing(self, releases):
+    def release_missing(self, releases: List[Sha1Git]) -> Iterable[Sha1Git]:
         return self._cql_runner.release_missing(releases)
 
     def release_get(self, releases):
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
@@ -582,7 +582,7 @@
 
         return {"release:add": len(to_add)}
 
-    def release_missing(self, releases):
+    def release_missing(self, releases: List[Sha1Git]) -> Iterable[Sha1Git]:
         yield from (rel for rel in releases if rel not in self._releases)
 
     def release_get(self, releases):
diff --git a/swh/storage/interface.py b/swh/storage/interface.py
--- a/swh/storage/interface.py
+++ b/swh/storage/interface.py
@@ -606,13 +606,13 @@
         ...
 
     @remote_api_endpoint("release/missing")
-    def release_missing(self, releases):
-        """List releases missing from storage
+    def release_missing(self, releases: List[Sha1Git]) -> Iterable[Sha1Git]:
+        """List missing release ids from storage
 
         Args:
-            releases: an iterable of release ids
+            releases: release ids
 
-        Returns:
+        Yields:
             a list of missing release ids
 
         """
diff --git a/swh/storage/storage.py b/swh/storage/storage.py
--- a/swh/storage/storage.py
+++ b/swh/storage/storage.py
@@ -680,7 +680,9 @@
 
     @timed
     @db_transaction_generator()
-    def release_missing(self, releases, db=None, cur=None):
+    def release_missing(
+        self, releases: List[Sha1Git], db=None, cur=None
+    ) -> Iterable[Sha1Git]:
         if not releases:
             return