diff --git a/smack-core/src/main/java/org/jivesoftware/smack/packet/Packet.java b/smack-core/src/main/java/org/jivesoftware/smack/packet/Packet.java
index 1529404b8..0fbd14a32 100644
--- a/smack-core/src/main/java/org/jivesoftware/smack/packet/Packet.java
+++ b/smack-core/src/main/java/org/jivesoftware/smack/packet/Packet.java
@@ -354,7 +354,7 @@ public abstract class Packet extends TopLevelStreamElement {
      * @return the extension sub-packets as XML or the Empty String if there
      * are no packet extensions.
      */
-    protected synchronized CharSequence getExtensionsXML() {
+    protected final XmlStringBuilder getExtensionsXML() {
         XmlStringBuilder xml = new XmlStringBuilder();
         // Add in all standard extension sub-packets.
         for (PacketExtension extension : getExtensions()) {