diff --git a/java/google/registry/model/billing/RegistrarCredit.java b/java/google/registry/model/billing/RegistrarCredit.java
index 497453cc3..c05daf88b 100644
--- a/java/google/registry/model/billing/RegistrarCredit.java
+++ b/java/google/registry/model/billing/RegistrarCredit.java
@@ -55,7 +55,7 @@ public final class RegistrarCredit extends ImmutableObject implements Buildable
     PROMOTION("Promotional Credit");
 
     /** A descriptive name for a credit of this type. */
-    private String descriptiveName;
+    private final String descriptiveName;
 
     CreditType(String descriptiveName) {
       this.descriptiveName = descriptiveName;