diff --git a/source/org/jivesoftware/smack/sasl/SASLMechanism.java b/source/org/jivesoftware/smack/sasl/SASLMechanism.java
index d42375f4e..2b775456a 100644
--- a/source/org/jivesoftware/smack/sasl/SASLMechanism.java
+++ b/source/org/jivesoftware/smack/sasl/SASLMechanism.java
@@ -79,7 +79,9 @@ public abstract class SASLMechanism {
         StringBuffer stanza = new StringBuffer();
         stanza.append("<response xmlns=\"urn:ietf:params:xml:ns:xmpp-sasl\">");
         String authenticationText = getChallengeResponse(StringUtils.decodeBase64(challenge));
-        stanza.append(StringUtils.encodeBase64(authenticationText));
+        if (authenticationText != null) {
+            stanza.append(StringUtils.encodeBase64(authenticationText));
+        }
         stanza.append("</response>");
 
         // Send the authentication to the server