diff --git a/libguile/fports.c b/libguile/fports.c
index de788c9..53d1140 100644
--- a/libguile/fports.c
+++ b/libguile/fports.c
@@ -1,4 +1,4 @@
-/* Copyright (C) 1995,1996,1997,1998,1999,2000,2001, 2002, 2003, 2004, 2006, 2007, 2008 Free Software Foundation, Inc.
+/* Copyright (C) 1995,1996,1997,1998,1999,2000,2001, 2002, 2003, 2004, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
  * 
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public License
@@ -671,8 +671,8 @@ fport_seek_or_seek64 (SCM port, off_t_or_off64_t offset, int whence)
    fport_seek already.  */
 
 #if GUILE_USE_64_CALLS && HAVE_STAT64 && SIZEOF_OFF_T != SIZEOF_OFF64_T
-static off_t
-fport_seek (SCM port, off_t offset, int whence)
+static scm_t_off
+fport_seek (SCM port, scm_t_off offset, int whence)
 {
   off64_t rv = fport_seek_or_seek64 (port, (off64_t) offset, whence);
   if (rv > OFF_T_MAX || rv < OFF_T_MIN)
@@ -696,7 +696,7 @@ scm_i_fport_seek (SCM port, SCM offset, int how)
 }
 
 static void
-fport_truncate (SCM port, off_t length)
+fport_truncate (SCM port, scm_t_off length)
 {
   scm_t_fport *fp = SCM_FSTREAM (port);
 
diff --git a/libguile/gen-scmconfig.c b/libguile/gen-scmconfig.c
index 85ebfae..9715973 100644
--- a/libguile/gen-scmconfig.c
+++ b/libguile/gen-scmconfig.c
@@ -400,6 +400,22 @@ main (int argc, char *argv[])
   pf ("#define SCM_HAVE_READDIR64_R 0 /* 0 or 1 */\n");
 #endif
 
+  /* Arrange so that we have a file offset type that reflects the one
+     used when compiling Guile, regardless of the application's
+     `_FILE_OFFSET_BITS' says.
+
+     Note that we can't define `scm_t_off' in terms of `off_t' or
+     `off64_t' because they may or may not be available depending on
+     how the application that uses Guile is compiled.  */
+
+#if defined GUILE_USE_64_CALLS && defined HAVE_STAT64
+  pf ("typedef scm_t_int64 scm_t_off;\n");
+#elif SIZEOF_OFF_T == SIZEOF_INT
+  pf ("typedef int scm_t_off;\n");
+#else
+  pf ("typedef long int scm_t_off;\n");
+#endif
+
 #if USE_DLL_IMPORT
   pf ("\n");
   pf ("/* Define some additional CPP macros on Win32 platforms. */\n");
diff --git a/libguile/ports.c b/libguile/ports.c
index 248e0a4..1b7c9a5 100644
--- a/libguile/ports.c
+++ b/libguile/ports.c
@@ -222,15 +222,14 @@ scm_set_port_close (scm_t_bits tc, int (*close) (SCM))
 }
 
 void
-scm_set_port_seek (scm_t_bits tc, off_t (*seek) (SCM port,
-					   off_t OFFSET,
-					   int WHENCE))
+scm_set_port_seek (scm_t_bits tc,
+		   scm_t_off (*seek) (SCM, scm_t_off, int))
 {
   scm_ptobs[SCM_TC2PTOBNUM (tc)].seek = seek;
 }
 
 void
-scm_set_port_truncate (scm_t_bits tc, void (*truncate) (SCM port, off_t length))
+scm_set_port_truncate (scm_t_bits tc, void (*truncate) (SCM, scm_t_off))
 {
   scm_ptobs[SCM_TC2PTOBNUM (tc)].truncate = truncate;
 }
diff --git a/libguile/ports.h b/libguile/ports.h
index 64a0a89..48ed770 100644
--- a/libguile/ports.h
+++ b/libguile/ports.h
@@ -29,8 +29,6 @@
 #include "libguile/struct.h"
 #include "libguile/threads.h"
 
-/* Not sure if this is a good idea.  We need it for off_t.  */
-#include <sys/types.h>
 
 
 
@@ -70,7 +68,7 @@ typedef struct
   unsigned char *read_buf;	/* buffer start.  */
   const unsigned char *read_pos;/* the next unread char.  */
   unsigned char *read_end;      /* pointer to last buffered char + 1.  */
-  off_t read_buf_size;		/* size of the buffer.  */
+  scm_t_off read_buf_size;		/* size of the buffer.  */
 
   /* when chars are put back into the buffer, e.g., using peek-char or
      unread-string, the read-buffer pointers are switched to cbuf.
@@ -79,7 +77,7 @@ typedef struct
   unsigned char *saved_read_buf;
   const unsigned char *saved_read_pos;
   unsigned char *saved_read_end;
-  off_t saved_read_buf_size;
+  scm_t_off saved_read_buf_size;
 
   /* write requests are saved into this buffer at write_pos until it
      reaches write_buf + write_buf_size, then the ptob flush is
@@ -88,7 +86,7 @@ typedef struct
   unsigned char *write_buf;     /* buffer start.  */
   unsigned char *write_pos;     /* pointer to last buffered char + 1.  */
   unsigned char *write_end;     /* pointer to end of buffer + 1.  */
-  off_t write_buf_size;		/* size of the buffer.  */
+  scm_t_off write_buf_size;		/* size of the buffer.  */
 
   unsigned char shortbuf;       /* buffer for "unbuffered" streams.  */
 
@@ -185,8 +183,8 @@ typedef struct scm_t_ptob_descriptor
   int (*fill_input) (SCM port);
   int (*input_waiting) (SCM port);
 
-  off_t (*seek) (SCM port, off_t OFFSET, int WHENCE);
-  void (*truncate) (SCM port, off_t length);
+  scm_t_off (*seek) (SCM port, scm_t_off OFFSET, int WHENCE);
+  void (*truncate) (SCM port, scm_t_off length);
 
 } scm_t_ptob_descriptor;
 
@@ -224,12 +222,12 @@ SCM_API void scm_set_port_end_input (scm_t_bits tc,
 				     void (*end_input) (SCM port,
 							int offset));
 SCM_API void scm_set_port_seek (scm_t_bits tc,
-				off_t (*seek) (SCM port,
-					       off_t OFFSET,
+				scm_t_off (*seek) (SCM port,
+					       scm_t_off OFFSET,
 					       int WHENCE));
 SCM_API void scm_set_port_truncate (scm_t_bits tc,
 				    void (*truncate) (SCM port,
-						      off_t length));
+						      scm_t_off length));
 SCM_API void scm_set_port_input_waiting (scm_t_bits tc, int (*input_waiting) (SCM));
 SCM_API SCM scm_char_ready_p (SCM port);
 size_t scm_take_from_input_buffers (SCM port, char *dest, size_t read_len);
diff --git a/libguile/r6rs-ports.c b/libguile/r6rs-ports.c
index d77c214..4b6a251 100644
--- a/libguile/r6rs-ports.c
+++ b/libguile/r6rs-ports.c
@@ -125,8 +125,8 @@ bip_fill_input (SCM port)
   return result;
 }
 
-static off_t
-bip_seek (SCM port, off_t offset, int whence)
+static scm_t_off
+bip_seek (SCM port, scm_t_off offset, int whence)
 #define FUNC_NAME "bip_seek"
 {
   off_t c_result = 0;
@@ -217,8 +217,8 @@ cbp_mark (SCM port)
     return SCM_BOOL_F;
 }
 
-static off_t
-cbp_seek (SCM port, off_t offset, int whence)
+static scm_t_off
+cbp_seek (SCM port, scm_t_off offset, int whence)
 #define FUNC_NAME "cbp_seek"
 {
   SCM result;
@@ -885,8 +885,8 @@ bop_write (SCM port, const void *data, size_t size)
   buf->len = (buf->len > buf->pos) ? buf->len : buf->pos;
 }
 
-static off_t
-bop_seek (SCM port, off_t offset, int whence)
+static scm_t_off
+bop_seek (SCM port, scm_t_off offset, int whence)
 #define FUNC_NAME "bop_seek"
 {
   scm_t_bop_buffer *buf;
diff --git a/libguile/strports.c b/libguile/strports.c
index 3f8a22e..4f816f2 100644
--- a/libguile/strports.c
+++ b/libguile/strports.c
@@ -1,4 +1,4 @@
-/* Copyright (C) 1995,1996,1998,1999,2000,2001,2002, 2003, 2005, 2006 Free Software Foundation, Inc.
+/* Copyright (C) 1995,1996,1998,1999,2000,2001,2002, 2003, 2005, 2006, 2009 Free Software Foundation, Inc.
  * 
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public License
@@ -199,8 +199,8 @@ st_end_input (SCM port, int offset)
   pt->rw_active = SCM_PORT_NEITHER;
 }
 
-static off_t
-st_seek (SCM port, off_t offset, int whence)
+static scm_t_off
+st_seek (SCM port, scm_t_off offset, int whence)
 {
   scm_t_port *pt = SCM_PTAB_ENTRY (port);
   off_t target;
@@ -272,7 +272,7 @@ st_seek (SCM port, off_t offset, int whence)
 }
 
 static void
-st_truncate (SCM port, off_t length)
+st_truncate (SCM port, scm_t_off length)
 {
   scm_t_port *pt = SCM_PTAB_ENTRY (port);