diff --git a/services/brig/src/Brig/Options.hs b/services/brig/src/Brig/Options.hs
index 874fd3a4a1c..ad631e49325 100644
--- a/services/brig/src/Brig/Options.hs
+++ b/services/brig/src/Brig/Options.hs
@@ -604,6 +604,7 @@ data CustomerExtensions = CustomerExtensions
   }
   deriving (Show, FromJSON, Generic)
 
+-- | See also: "Galley.API.CustomBackend", `galley.custom_backend`.
 newtype DomainsBlockedForRegistration = DomainsBlockedForRegistration [Domain]
   deriving newtype (Show, FromJSON, Generic)
 
diff --git a/services/galley/src/Galley/API/CustomBackend.hs b/services/galley/src/Galley/API/CustomBackend.hs
index ebcff2b55e2..d65c6effe62 100644
--- a/services/galley/src/Galley/API/CustomBackend.hs
+++ b/services/galley/src/Galley/API/CustomBackend.hs
@@ -15,6 +15,7 @@
 -- You should have received a copy of the GNU Affero General Public License along
 -- with this program. If not, see <https://www.gnu.org/licenses/>.
 
+-- | See also: 'DomainsBlockedForRegistration'.
 module Galley.API.CustomBackend
   ( getCustomBackendByDomainH,
     internalPutCustomBackendByDomainH,