diff --git a/xds/src/main/java/io/grpc/xds/XdsNameResolver.java b/xds/src/main/java/io/grpc/xds/XdsNameResolver.java
index ac59f418987..7f9d2a6cd9b 100644
--- a/xds/src/main/java/io/grpc/xds/XdsNameResolver.java
+++ b/xds/src/main/java/io/grpc/xds/XdsNameResolver.java
@@ -148,7 +148,6 @@ private class ConfigWatcherImpl implements ConfigWatcher {
       this.listener = listener;
     }
 
-    @SuppressWarnings("unchecked")
     @Override
     public void onConfigChanged(ConfigUpdate update) {
       Map<String, ?> rawLbConfig;
@@ -220,7 +219,7 @@ public void onError(Status error) {
     }
   }
 
-  private static Map<String, ?> generateXdsRoutingRawConfig(List<Route> routesUpdate) {
+  private static ImmutableMap<String, ?> generateXdsRoutingRawConfig(List<Route> routesUpdate) {
     List<Object> routes = new ArrayList<>(routesUpdate.size());
     Map<String, Object> actions = new LinkedHashMap<>();
     Map<RouteAction, String> exitingActions = new HashMap<>();
@@ -275,7 +274,7 @@ public void onError(Status error) {
         ImmutableMap.of("route", routes, "action", actions));
   }
 
-  private static Map<String, ?> generateWeightedTargetRawConfig(
+  private static ImmutableMap<String, ?> generateWeightedTargetRawConfig(
       List<ClusterWeight> clusterWeights) {
     Map<String, Object> targets = new LinkedHashMap<>();
     for (ClusterWeight clusterWeight : clusterWeights) {
@@ -292,7 +291,7 @@ public void onError(Status error) {
         ImmutableMap.of("targets", targets));
   }
 
-  private static Map<String, ?> generateCdsRawConfig(String clusterName) {
+  private static ImmutableMap<String, ?> generateCdsRawConfig(String clusterName) {
     return ImmutableMap.of(XdsLbPolicies.CDS_POLICY_NAME, ImmutableMap.of("cluster", clusterName));
   }
 
diff --git a/xds/src/main/java/io/grpc/xds/internal/sds/SdsProtocolNegotiators.java b/xds/src/main/java/io/grpc/xds/internal/sds/SdsProtocolNegotiators.java
index c6fc2d94072..8270d2dad11 100644
--- a/xds/src/main/java/io/grpc/xds/internal/sds/SdsProtocolNegotiators.java
+++ b/xds/src/main/java/io/grpc/xds/internal/sds/SdsProtocolNegotiators.java
@@ -55,6 +55,10 @@
 @VisibleForTesting
 public final class SdsProtocolNegotiators {
 
+  // Prevent instantiation.
+  private SdsProtocolNegotiators() {
+  }
+
   private static final Logger logger = Logger.getLogger(SdsProtocolNegotiators.class.getName());
 
   private static final AsciiString SCHEME = AsciiString.of("https");