diff --git a/smack-core/src/main/java/org/jivesoftware/smack/util/XmlStringBuilder.java b/smack-core/src/main/java/org/jivesoftware/smack/util/XmlStringBuilder.java
index ae8b2931b..2e00eac68 100644
--- a/smack-core/src/main/java/org/jivesoftware/smack/util/XmlStringBuilder.java
+++ b/smack-core/src/main/java/org/jivesoftware/smack/util/XmlStringBuilder.java
@@ -628,7 +628,9 @@ public class XmlStringBuilder implements Appendable, CharSequence, Element {
 
     @Override
     public CharSequence toXML(XmlEnvironment enclosingXmlEnvironment) {
-        StringBuilder res = new StringBuilder();
+        // This is only the potential length, since the actual length depends on the given XmlEnvironment.
+        int potentialLength = length();
+        StringBuilder res = new StringBuilder(potentialLength);
         try {
             appendXmlTo(res, enclosingXmlEnvironment);
         } catch (IOException e) {