--- io.c.orig	2009-11-25 17:45:13.000000000 +0900
+++ io.c	2010-01-08 12:31:15.000000000 +0900
@@ -1297,8 +1297,15 @@
                 goto again;
             rb_sys_fail(fptr->path);
         }
-        if (fptr->f) /* update pos in FILE structure [ruby-core:21561] */
+        if (fptr->f) {
+#ifdef __SOFF
+	    fptr->f->_flags &= ~__SOFF;
+	    (void)io_tell(fptr);
+#else
+	    /* update pos in FILE structure [ruby-core:21561] */
             fflush(fptr->f);
+#endif
+	}
     }
     rb_str_resize(str, n);