Index: lucene/src/java/org/apache/lucene/store/MMapDirectory.java
===================================================================
--- lucene/src/java/org/apache/lucene/store/MMapDirectory.java	(revision 1059628)
+++ lucene/src/java/org/apache/lucene/store/MMapDirectory.java	(working copy)
@@ -79,7 +79,7 @@
  */
 public class MMapDirectory extends FSDirectory {
   private boolean useUnmapHack = UNMAP_SUPPORTED;
-  public static final int DEFAULT_MAX_BUFF = Constants.JRE_IS_64BIT ? Integer.MAX_VALUE : (256 * 1024 * 1024);
+  public static final int DEFAULT_MAX_BUFF = (Constants.JRE_IS_64BIT && !Constants.WINDOWS) ? Integer.MAX_VALUE : (256 * 1024 * 1024);
   private int maxBBuf = DEFAULT_MAX_BUFF;
 
   /** Create a new MMapDirectory for the named location.
@@ -176,12 +176,13 @@
   
   /**
    * Sets the maximum chunk size (default is {@link Integer#MAX_VALUE} for
-   * 64 bit JVMs and 256 MiBytes for 32 bit JVMs) used for memory mapping.
+   * 64 bit non-Windows JVMs and 256 MiBytes for 32 bit and Windows JVMs) 
+   * used for memory mapping.
    * Especially on 32 bit platform, the address space can be very fragmented,
    * so large index files cannot be mapped.
    * Using a lower chunk size makes the directory implementation a little
    * bit slower (as the correct chunk must be resolved on each seek)
-   * but the chance is higher that mmap does not fail. On 64 bit
+   * but the chance is higher that mmap does not fail. On 64 bit non-Windows
    * Java platforms, this parameter should always be {@link Integer#MAX_VALUE},
    * as the address space is big enough.
    */