diff --git a/src/main/java/eu/siacs/conversations/entities/Message.java b/src/main/java/eu/siacs/conversations/entities/Message.java
index 44b8db691..44f7588f8 100644
--- a/src/main/java/eu/siacs/conversations/entities/Message.java
+++ b/src/main/java/eu/siacs/conversations/entities/Message.java
@@ -7,6 +7,7 @@ import android.text.SpannableStringBuilder;
 import android.util.Log;
 
 import com.google.common.base.Strings;
+import com.google.common.collect.ImmutableSet;
 
 import org.json.JSONException;
 
@@ -534,7 +535,7 @@ public class Message extends AbstractEntity implements AvatarService.Avatarable
 	}
 
 	public Set<ReadByMarker> getReadByMarkers() {
-		return Collections.unmodifiableSet(this.readByMarkers);
+		return ImmutableSet.copyOf(this.readByMarkers);
 	}
 
 	boolean similar(Message message) {