diff --git a/cluster/src/main/java/io/scalecube/cluster/gossip/GossipRequest.java b/cluster/src/main/java/io/scalecube/cluster/gossip/GossipRequest.java
index 4f0b2f95..458f2d3e 100644
--- a/cluster/src/main/java/io/scalecube/cluster/gossip/GossipRequest.java
+++ b/cluster/src/main/java/io/scalecube/cluster/gossip/GossipRequest.java
@@ -27,7 +27,7 @@ public GossipRequest(Gossip gossip, String from) {
   public GossipRequest(List<Gossip> gossips, String from) {
     Objects.requireNonNull(gossips);
     Objects.requireNonNull(from);
-    this.gossips = new ArrayList<>(gossips);
+    this.gossips = Collections.unmodifiableList(new ArrayList<>(gossips));
     this.from = from;
   }
 
@@ -53,11 +53,12 @@ public void writeExternal(ObjectOutput out) throws IOException {
   @Override
   public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
     // gossips
-    int size = in.readInt();
-    gossips = new ArrayList<>(size);
-    for (int i = 0; i < size; i++) {
+    int gossipsSize = in.readInt();
+    List<Gossip> gossips = new ArrayList<>(gossipsSize);
+    for (int i = 0; i < gossipsSize; i++) {
       gossips.add((Gossip) in.readObject());
     }
+    this.gossips = Collections.unmodifiableList(gossips);
     // from
     from = in.readUTF();
   }
diff --git a/cluster/src/main/java/io/scalecube/cluster/membership/SyncData.java b/cluster/src/main/java/io/scalecube/cluster/membership/SyncData.java
index c4b984e8..fbb66118 100644
--- a/cluster/src/main/java/io/scalecube/cluster/membership/SyncData.java
+++ b/cluster/src/main/java/io/scalecube/cluster/membership/SyncData.java
@@ -6,6 +6,7 @@
 import java.io.ObjectOutput;
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.List;
 import java.util.Objects;
 import java.util.StringJoiner;
@@ -31,12 +32,12 @@ public SyncData() {}
   public SyncData(Collection<MembershipRecord> membership, String syncGroup) {
     Objects.requireNonNull(membership);
     Objects.requireNonNull(syncGroup);
-    this.membership = new ArrayList<>(membership);
+    this.membership = Collections.unmodifiableList(new ArrayList<>(membership));
     this.syncGroup = syncGroup;
   }
 
   public Collection<MembershipRecord> getMembership() {
-    return new ArrayList<>(membership);
+    return membership;
   }
 
   public String getSyncGroup() {
@@ -57,11 +58,12 @@ public void writeExternal(ObjectOutput out) throws IOException {
   @Override
   public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
     // membership
-    int size = in.readInt();
-    membership = new ArrayList<>(size);
-    for (int i = 0; i < size; i++) {
+    int membershipSize = in.readInt();
+    List<MembershipRecord> membership = new ArrayList<>(membershipSize);
+    for (int i = 0; i < membershipSize; i++) {
       membership.add((MembershipRecord) in.readObject());
     }
+    this.membership = Collections.unmodifiableList(membership);
     // syncGroup
     syncGroup = in.readUTF();
   }
diff --git a/transport-parent/transport-api/src/main/java/io/scalecube/cluster/transport/api/Message.java b/transport-parent/transport-api/src/main/java/io/scalecube/cluster/transport/api/Message.java
index a121d1c5..d6e5e159 100644
--- a/transport-parent/transport-api/src/main/java/io/scalecube/cluster/transport/api/Message.java
+++ b/transport-parent/transport-api/src/main/java/io/scalecube/cluster/transport/api/Message.java
@@ -217,13 +217,14 @@ public void writeExternal(ObjectOutput out) throws IOException {
   @Override
   public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
     // headers
-    int size = in.readInt();
-    headers = new HashMap<>(size);
-    for (int i = 0; i < size; i++) {
+    int headersSize = in.readInt();
+    Map<String, String> headers = new HashMap<>(headersSize);
+    for (int i = 0; i < headersSize; i++) {
       String name = in.readUTF();
       String value = in.readUTF();
       headers.put(name, value);
     }
+    this.headers = Collections.unmodifiableMap(headers);
     // data
     data = in.readObject();
   }