diff --git a/libtransmission/inout.c b/libtransmission/inout.c
index f2d16c831..aaf08dd69 100644
--- a/libtransmission/inout.c
+++ b/libtransmission/inout.c
@@ -195,13 +195,13 @@ tr_ioRead( tr_torrent  * tor,
 }
 
 int
-tr_ioWrite( tr_torrent  * tor,
-            int           pieceIndex,
-            int           begin,
-            int           len,
-            uint8_t     * buf )
+tr_ioWrite( tr_torrent     * tor,
+            int              pieceIndex,
+            int              begin,
+            int              len,
+            const uint8_t  * buf )
 {
-    return readOrWritePiece( tor, TR_IO_WRITE, pieceIndex, begin, buf, len );
+    return readOrWritePiece( tor, TR_IO_WRITE, pieceIndex, begin, (void*)buf, len );
 }
 
 /****
diff --git a/libtransmission/inout.h b/libtransmission/inout.h
index f3e319c60..b88c0d6c0 100644
--- a/libtransmission/inout.h
+++ b/libtransmission/inout.h
@@ -38,7 +38,7 @@ typedef struct tr_io tr_io;
  * TR_ERROR_IO_* otherwise.
  **********************************************************************/
 int tr_ioRead  ( struct tr_torrent*, int index, int begin, int len, uint8_t * );
-int tr_ioWrite ( struct tr_torrent *, int index, int begin, int len, uint8_t * );
+int tr_ioWrite ( struct tr_torrent *, int index, int begin, int len, const uint8_t * );
 
 /* hashes the specified piece and updates the completion accordingly. */
 int tr_ioHash ( tr_torrent*, int piece );