Index: java/org/apache/lucene/document/Field.java
===================================================================
--- java/org/apache/lucene/document/Field.java	(revision 636100)
+++ java/org/apache/lucene/document/Field.java	(working copy)
@@ -148,7 +148,7 @@
   /** The value of the field in Binary, or null.  If null, the Reader value,
    * String value, or TokenStream value is used. Exactly one of stringValue(), 
    * readerValue(), binaryValue(), and tokenStreamValue() must be set. */
-  public byte[] binaryValue()   { return fieldsData instanceof byte[] ? (byte[])fieldsData : null; }
+  public byte[] binaryValue()   { return isBinary ? (byte[])fieldsData : null; }
   
   /** The value of the field as a TokesStream, or null.  If null, the Reader value,
    * String value, or binary value is used. Exactly one of stringValue(), 
Index: java/org/apache/lucene/index/FieldsReader.java
===================================================================
--- java/org/apache/lucene/index/FieldsReader.java	(revision 636100)
+++ java/org/apache/lucene/index/FieldsReader.java	(working copy)
@@ -426,11 +426,12 @@
           } else {
             fieldsData = b;
           }
+          this.isBinary = true;
         } catch (IOException e) {
           throw new FieldReaderException(e);
         }
       }
-      return fieldsData instanceof byte[] ? (byte[]) fieldsData : null;
+      return this.isBinary ? (byte[]) fieldsData : null;
     }
 
     /** The value of the field as a Reader, or null.  If null, the String value,