diff --git a/include/nuttx/mtd/mtd.h b/include/nuttx/mtd/mtd.h
index b2a192c9756..4162cde6f9f 100644
--- a/include/nuttx/mtd/mtd.h
+++ b/include/nuttx/mtd/mtd.h
@@ -2,7 +2,7 @@
  * include/nuttx/mtd/mtd.h
  * Memory Technology Device (MTD) interface
  *
- *   Copyright (C) 2009-2013 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2009-2013, 2015 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -83,10 +83,11 @@
 
 struct mtd_geometry_s
 {
-  uint32_t blocksize :14; /* Size of one read/write block.  Largest: 16KB-1 */
-  uint32_t erasesize :18; /* Size of one erase blocks -- must be a multiple
-                           * of blocksize.  Largest: 512KB-1 */
-  size_t neraseblocks;    /* Number of erase blocks */
+  uint16_t blocksize;     /* Size of one read/write block. */
+                          /* Probably 16-bits wasted here for alignment */
+  uint32_t erasesize;     /* Size of one erase blocks -- must be a multiple
+                           * of blocksize.*/
+  uint32_t neraseblocks;  /* Number of erase blocks */
 };
 
 /* The following defines the information for writing bytes to a sector