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
@@ -755,7 +755,9 @@
         assert len(origins) <= limit
         return PagedResult(results=origins, next_page_token=next_page_token)
 
-    def origin_count(self, url_pattern, regexp=False, with_visit=False):
+    def origin_count(
+        self, url_pattern: str, regexp: bool = False, with_visit: bool = False
+    ) -> int:
         actual_page = self.origin_search(
             url_pattern, regexp=regexp, with_visit=with_visit, limit=len(self._origins),
         )
diff --git a/swh/storage/interface.py b/swh/storage/interface.py
--- a/swh/storage/interface.py
+++ b/swh/storage/interface.py
@@ -1067,7 +1067,9 @@
 
     @deprecated
     @remote_api_endpoint("origin/count")
-    def origin_count(self, url_pattern, regexp=False, with_visit=False):
+    def origin_count(
+        self, url_pattern: str, regexp: bool = False, with_visit: bool = False
+    ) -> int:
         """Count origins whose urls contain a provided string pattern
         or match a provided regular expression.
         The pattern search in origin urls is performed in a case insensitive
diff --git a/swh/storage/storage.py b/swh/storage/storage.py
--- a/swh/storage/storage.py
+++ b/swh/storage/storage.py
@@ -1142,8 +1142,13 @@
     @timed
     @db_transaction()
     def origin_count(
-        self, url_pattern, regexp=False, with_visit=False, db=None, cur=None
-    ):
+        self,
+        url_pattern: str,
+        regexp: bool = False,
+        with_visit: bool = False,
+        db=None,
+        cur=None,
+    ) -> int:
         return db.origin_count(url_pattern, regexp, with_visit, cur)
 
     @timed