Index: modules/analysis/common/src/java/org/apache/lucene/analysis/en/KStemmer.java
===================================================================
--- modules/analysis/common/src/java/org/apache/lucene/analysis/en/KStemmer.java	(revision 1134263)
+++ modules/analysis/common/src/java/org/apache/lucene/analysis/en/KStemmer.java	(working copy)
@@ -1372,7 +1372,8 @@
     if (s != null) return s;
     return word.toString();
   }
-  
+
+  /** @lucene.internal Returns the stem, or null if the stem is in the char[] returned by getChars()/getLength() */
   String getString() {
     return result;
   }
Index: modules/analysis/common/src/java/org/apache/lucene/analysis/en/KStemFilter.java
===================================================================
--- modules/analysis/common/src/java/org/apache/lucene/analysis/en/KStemFilter.java	(revision 1134263)
+++ modules/analysis/common/src/java/org/apache/lucene/analysis/en/KStemFilter.java	(working copy)
@@ -55,8 +55,15 @@
     char[] term = termAttribute.buffer();
     int len = termAttribute.length();
     if ((!keywordAtt.isKeyword()) && stemmer.stem(term, len)) {
-      char[] chars = stemmer.asString().toCharArray();
-      termAttribute.copyBuffer(chars, 0, chars.length);
+      String result = stemmer.getString();
+      if (result != null) {
+        int stemLen = result.length();
+        termAttribute.resizeBuffer(stemLen);
+        termAttribute.setLength(stemLen);
+        result.getChars(0, stemLen, termAttribute.buffer(), 0);
+      } else {
+        termAttribute.copyBuffer(stemmer.getChars(), 0, stemmer.getLength());
+      }
     }
 
     return true;