Index: src/test/org/apache/lucene/index/TestIndexWriter.java
===================================================================
--- src/test/org/apache/lucene/index/TestIndexWriter.java	(revision 1039740)
+++ src/test/org/apache/lucene/index/TestIndexWriter.java	(working copy)
@@ -49,6 +49,8 @@
 import org.apache.lucene.analysis.tokenattributes.PositionIncrementAttribute;
 import org.apache.lucene.document.Document;
 import org.apache.lucene.document.Field;
+import org.apache.lucene.search.Similarity;
+import org.apache.lucene.search.SimilarityDelegator;
 import org.apache.lucene.search.IndexSearcher;
 import org.apache.lucene.search.PhraseQuery;
 import org.apache.lucene.search.Query;
@@ -4942,4 +4944,21 @@
 
     dir.close();
   }
+
+  public void testCustomSimilarity() throws Exception {
+    Directory dir = new RAMDirectory();
+    IndexWriter w = new IndexWriter(dir, new WhitespaceAnalyzer(), IndexWriter.MaxFieldLength.UNLIMITED);
+    final boolean[] called = new boolean[1];
+    w.setSimilarity(new SimilarityDelegator(Similarity.getDefault()) {
+        public float lengthNorm(String fieldName, int numTerms) {
+          called[0] = true;
+          return super.lengthNorm(fieldName, numTerms);
+        }
+      });
+    Document doc = new Document();
+    doc.add(new Field("f", "some text", Field.Store.NO, Field.Index.ANALYZED));
+    w.addDocument(doc);
+    w.close();
+    assertTrue(called[0]);
+  }
 }