diff --git a/services/domain/Big.Infrastructure/InMemoryRegistrationStore.cs b/services/domain/Big.Infrastructure/InMemoryRegistrationStore.cs
index 75e630c..68a6590 100644
--- a/services/domain/Big.Infrastructure/InMemoryRegistrationStore.cs
+++ b/services/domain/Big.Infrastructure/InMemoryRegistrationStore.cs
@@ -29,5 +29,6 @@ public sealed class InMemoryRegistrationStore : IRegistrationStore
 
     public Task<IReadOnlyList<Registration>> FindDueForHerregistratieReminderAsync(
         DateTimeOffset asOf, CancellationToken ct = default)
-        => Task.FromResult<IReadOnlyList<Registration>>([]); // RED stub
+        => Task.FromResult<IReadOnlyList<Registration>>(
+            _byId.Values.Where(r => r.HerregistratieReminderDue(asOf)).ToList());
 }