diff --git a/server/src/main/java/org/elasticsearch/cluster/DiffableUtils.java b/server/src/main/java/org/elasticsearch/cluster/DiffableUtils.java
index 6483126ac80ee..8749397323fdf 100644
--- a/server/src/main/java/org/elasticsearch/cluster/DiffableUtils.java
+++ b/server/src/main/java/org/elasticsearch/cluster/DiffableUtils.java
@@ -16,6 +16,7 @@
 
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -242,7 +243,7 @@ public Map<K, T> apply(Map<K, T> map) {
                 builder.put(upsert.getKey(), upsert.getValue());
             }
 
-            return builder;
+            return Collections.unmodifiableMap(builder);
         }
     }
 
diff --git a/server/src/main/java/org/elasticsearch/cluster/metadata/Metadata.java b/server/src/main/java/org/elasticsearch/cluster/metadata/Metadata.java
index f3e3a7979bd1c..4286a915e36c9 100644
--- a/server/src/main/java/org/elasticsearch/cluster/metadata/Metadata.java
+++ b/server/src/main/java/org/elasticsearch/cluster/metadata/Metadata.java
@@ -1214,8 +1214,8 @@ public Metadata apply(Metadata part) {
             builder.indices(updatedIndices);
             builder.templates(templates.apply(part.templates));
             builder.customs(customs.apply(part.customs));
-            builder.put(Collections.unmodifiableMap(immutableStateMetadata.apply(part.immutableStateMetadata)));
-            return builder.build(true);
+            builder.put(immutableStateMetadata.apply(part.immutableStateMetadata));
+            return builder.build();
         }
     }