Index: lucene/analysis/common/src/java/org/apache/lucene/analysis/synonym/SynonymMap.java
===================================================================
--- lucene/analysis/common/src/java/org/apache/lucene/analysis/synonym/SynonymMap.java	(revision 1457376)
+++ lucene/analysis/common/src/java/org/apache/lucene/analysis/synonym/SynonymMap.java	(working copy)
@@ -90,26 +90,21 @@
     public static CharsRef join(String[] words, CharsRef reuse) {
       int upto = 0;
       char[] buffer = reuse.chars;
-      for(String word : words) {
-        if (upto > 0) {
-          if (upto >= buffer.length) {
-            reuse.grow(upto);
-            buffer = reuse.chars;
-          }
-          buffer[upto++] = SynonymMap.WORD_SEPARATOR;
-        }
-
-        final int wordLen =  word.length();
-        final int needed = upto + wordLen;
+      for (String word : words) {
+        final int wordLen = word.length();
+        final int needed = (0 == upto ? wordLen : 1 + upto + wordLen); // Add 1 for WORD_SEPARATOR
         if (needed > buffer.length) {
           reuse.grow(needed);
           buffer = reuse.chars;
         }
+        if (upto > 0) {
+          buffer[upto++] = SynonymMap.WORD_SEPARATOR;
+        }
 
         word.getChars(0, wordLen, buffer, upto);
         upto += wordLen;
       }
-
+      reuse.length = upto;
       return reuse;
     }
     
Index: lucene/analysis/common/src/test/org/apache/lucene/analysis/synonym/TestSynonymMapFilter.java
===================================================================
--- lucene/analysis/common/src/test/org/apache/lucene/analysis/synonym/TestSynonymMapFilter.java	(revision 1457376)
+++ lucene/analysis/common/src/test/org/apache/lucene/analysis/synonym/TestSynonymMapFilter.java	(working copy)
@@ -55,9 +55,13 @@
     if (VERBOSE) {
       System.out.println("  add input=" + input + " output=" + output + " keepOrig=" + keepOrig);
     }
-    b.add(new CharsRef(input.replaceAll(" +", "\u0000")),
-          new CharsRef(output.replaceAll(" +", "\u0000")),
-          keepOrig);
+    CharsRef inputCharsRef = new CharsRef();
+    SynonymMap.Builder.join(input.split(" +"), inputCharsRef);
+
+    CharsRef outputCharsRef = new CharsRef();
+    SynonymMap.Builder.join(output.split(" +"), outputCharsRef);
+
+    b.add(inputCharsRef, outputCharsRef, keepOrig);
   }
 
   private void assertEquals(CharTermAttribute term, String expected) {