diff --git a/src/main/java/com/googlesource/gerrit/plugins/multisite/validation/dfsrefdb/DefaultSharedRefEnforcement.java b/src/main/java/com/googlesource/gerrit/plugins/multisite/validation/dfsrefdb/DefaultSharedRefEnforcement.java
index 6b495fb..63bab09 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/multisite/validation/dfsrefdb/DefaultSharedRefEnforcement.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/multisite/validation/dfsrefdb/DefaultSharedRefEnforcement.java
@@ -16,11 +16,10 @@
 
 import com.google.common.base.MoreObjects;
 import com.google.common.collect.ImmutableMap;
-import java.util.Map;
 
 public class DefaultSharedRefEnforcement implements SharedRefEnforcement {
 
-  private static final Map<String, EnforcePolicy> PREDEF_ENFORCEMENTS =
+  private static final ImmutableMap<String, EnforcePolicy> PREDEF_ENFORCEMENTS =
       ImmutableMap.of("All-Users:refs/meta/external-ids", EnforcePolicy.DESIRED);
 
   @Override