diff --git a/lib/membership_fees/changes/validate_same_interval.ex b/lib/membership_fees/changes/validate_same_interval.ex
index 213efb8..db2ff3f 100644
--- a/lib/membership_fees/changes/validate_same_interval.ex
+++ b/lib/membership_fees/changes/validate_same_interval.ex
@@ -62,10 +62,10 @@ defmodule Mv.MembershipFees.Changes.ValidateSameInterval do
           add_interval_mismatch_error(changeset, current_interval, new_interval)
         end
 
-      {:error, _reason} ->
-        # If we can't load the types, allow the change (fail open)
-        # The database constraint will catch invalid foreign keys
-        changeset
+      {:error, reason} ->
+        # Fail closed: If we can't load the types, reject the change
+        # This prevents inconsistent data states
+        add_type_validation_error(changeset, reason)
     end
   end
 
@@ -114,6 +114,17 @@ defmodule Mv.MembershipFees.Changes.ValidateSameInterval do
     )
   end
 
+  # Add validation error when types cannot be loaded
+  defp add_type_validation_error(changeset, reason) do
+    message = "Could not validate membership fee type intervals: type not found"
+
+    Ash.Changeset.add_error(
+      changeset,
+      field: :membership_fee_type_id,
+      message: message
+    )
+  end
+
   # Format interval atom to human-readable string
   defp format_interval(:monthly), do: "monthly"
   defp format_interval(:quarterly), do: "quarterly"