diff --git a/java/google/registry/cron/TldFanoutAction.java b/java/google/registry/cron/TldFanoutAction.java
index bb67a159b..6df61a35b 100644
--- a/java/google/registry/cron/TldFanoutAction.java
+++ b/java/google/registry/cron/TldFanoutAction.java
@@ -79,14 +79,15 @@ public final class TldFanoutAction implements Runnable {
   private static final String JITTER_SECONDS_PARAM = "jitterSeconds";
 
   /** A set of control params to TldFanoutAction that aren't passed down to the executing action. */
-  private static final Set<String> CONTROL_PARAMS = ImmutableSet.of(
-      ENDPOINT_PARAM,
-      QUEUE_PARAM,
-      FOR_EACH_REAL_TLD_PARAM,
-      FOR_EACH_TEST_TLD_PARAM,
-      RUN_IN_EMPTY_PARAM,
-      EXCLUDE_PARAM,
-      JITTER_SECONDS_PARAM);
+  private static final ImmutableSet<String> CONTROL_PARAMS =
+      ImmutableSet.of(
+          ENDPOINT_PARAM,
+          QUEUE_PARAM,
+          FOR_EACH_REAL_TLD_PARAM,
+          FOR_EACH_TEST_TLD_PARAM,
+          RUN_IN_EMPTY_PARAM,
+          EXCLUDE_PARAM,
+          JITTER_SECONDS_PARAM);
 
   private static final String TLD_PATHARG = ":tld";
   private static final Random random = new Random();
diff --git a/java/google/registry/model/domain/rgp/GracePeriodStatus.java b/java/google/registry/model/domain/rgp/GracePeriodStatus.java
index 6a8b509ae..ab0c85a6f 100644
--- a/java/google/registry/model/domain/rgp/GracePeriodStatus.java
+++ b/java/google/registry/model/domain/rgp/GracePeriodStatus.java
@@ -19,11 +19,11 @@ import static com.google.common.base.Predicates.not;
 import static java.util.Arrays.asList;
 
 import com.google.common.base.Function;
+import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.Iterables;
 import com.google.common.collect.Maps;
 import google.registry.model.translators.EnumToAttributeAdapter;
 import google.registry.model.translators.EnumToAttributeAdapter.EppEnum;
-import java.util.Map;
 import javax.annotation.Nullable;
 import javax.xml.bind.annotation.XmlAttribute;
 import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
@@ -100,7 +100,7 @@ public enum GracePeriodStatus implements EppEnum {
   TRANSFER("transferPeriod");
 
   /** Provide a quick lookup of GracePeriodStatus from XML name. */
-  private static final Map<String, GracePeriodStatus> XML_NAME_TO_GRACE_PERIOD_STATUS =
+  private static final ImmutableMap<String, GracePeriodStatus> XML_NAME_TO_GRACE_PERIOD_STATUS =
       Maps.uniqueIndex(
           // SUNRUSH_ADD isn't a real grace period type visible in EPP XML, so exclude it.
           Iterables.filter(asList(GracePeriodStatus.values()), not(equalTo(SUNRUSH_ADD))),
diff --git a/java/google/registry/monitoring/whitebox/MetricsExportAction.java b/java/google/registry/monitoring/whitebox/MetricsExportAction.java
index 9a03473e9..19ac025d4 100644
--- a/java/google/registry/monitoring/whitebox/MetricsExportAction.java
+++ b/java/google/registry/monitoring/whitebox/MetricsExportAction.java
@@ -39,7 +39,6 @@ import google.registry.request.ParameterMap;
 import google.registry.util.FormattingLogger;
 import java.io.IOException;
 import java.util.Map;
-import java.util.Set;
 import javax.inject.Inject;
 
 /** Action for exporting metrics to BigQuery. */
@@ -49,7 +48,7 @@ public class MetricsExportAction implements Runnable {
   public static final String PATH = "/_dr/task/metrics";
   private static final FormattingLogger logger = getLoggerForCallerClass();
   private static final String DATASET_ID = "metrics";
-  private static final Set<String> SPECIAL_PARAMS = ImmutableSet.of("tableId", "insertId");
+  private static final ImmutableSet<String> SPECIAL_PARAMS = ImmutableSet.of("tableId", "insertId");
 
   @Inject @Parameter("tableId") String tableId;
   @Inject @Parameter("insertId") String insertId;