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
@@ -1133,7 +1133,7 @@
             metadata: JSON-encodable object
 
         Returns:
-            dict: same as args, plus an 'id' key.
+            an identifier of the provider
         """
         provider = {
                 'name': provider_name,
@@ -1144,7 +1144,7 @@
         key = self._metadata_provider_key(provider)
         provider['id'] = key
         self._metadata_providers[key] = provider
-        return provider.copy()
+        return key
 
     def metadata_provider_get(self, provider_id, db=None, cur=None):
         """Get a metadata provider
diff --git a/swh/storage/storage.py b/swh/storage/storage.py
--- a/swh/storage/storage.py
+++ b/swh/storage/storage.py
@@ -1386,7 +1386,7 @@
             metadata: JSON-encodable object
 
         Returns:
-            dict: same as args, plus an 'id' key.
+            int: an identifier of the provider
         """
         return db.metadata_provider_add(provider_name, provider_type,
                                         provider_url, metadata, cur)
diff --git a/swh/storage/tests/test_storage.py b/swh/storage/tests/test_storage.py
--- a/swh/storage/tests/test_storage.py
+++ b/swh/storage/tests/test_storage.py
@@ -1821,7 +1821,7 @@
         # given
         origin_id = self.storage.origin_add([self.origin])[0]['id']
         origin_id2 = self.storage.origin_add([self.origin2])[0]['id']
-        self.storage.metadata_provider_add(
+        provider1_id = self.storage.metadata_provider_add(
                            self.provider['name'],
                            self.provider['type'],
                            self.provider['url'],
@@ -1830,8 +1830,10 @@
                             'provider_name': self.provider['name'],
                             'provider_url': self.provider['url']
                    })
+        self.assertEqual(provider1,
+                         self.storage.metadata_provider_get(provider1_id))
 
-        self.storage.metadata_provider_add(
+        provider2_id = self.storage.metadata_provider_add(
                             'swMATH',
                             'registry',
                             'http://www.swmath.org/',
@@ -1841,6 +1843,8 @@
                             'provider_name': 'swMATH',
                             'provider_url': 'http://www.swmath.org/'
                    })
+        self.assertEqual(provider2,
+                         self.storage.metadata_provider_get(provider2_id))
 
         # using the only tool now inserted in the data.sql, but for this
         # provider should be a crawler tool (not yet implemented)