diff --git a/lucene/core/src/java/org/apache/lucene/codecs/lucene3x/Lucene3xCodec.java b/lucene/core/src/java/org/apache/lucene/codecs/lucene3x/Lucene3xCodec.java
index 888c1b8..de98a51 100644
--- a/lucene/core/src/java/org/apache/lucene/codecs/lucene3x/Lucene3xCodec.java
+++ b/lucene/core/src/java/org/apache/lucene/codecs/lucene3x/Lucene3xCodec.java
@@ -76,12 +76,12 @@ public class Lucene3xCodec extends Codec {
   private final DocValuesFormat docValuesFormat = new DocValuesFormat() {
     @Override
     public PerDocConsumer docsConsumer(PerDocWriteState state) throws IOException {
-      return null;
+      throw new UnsupportedOperationException("this codec doesn't support DocValues");
     }
 
     @Override
     public PerDocProducer docsProducer(SegmentReadState state) throws IOException {
-      return null;
+      return null; // that if fine since null means simply no DocValues available
     }
 
     @Override