--- io.c.orig	2009-11-25 08:45:13.000000000 +0000
+++ io.c
@@ -488,7 +488,16 @@ io_fwrite(str, fptr)
 	r = write(fileno(f), RSTRING(str)->ptr+offset, l);
         TRAP_END;
 #if BSD_STDIO
-	fseeko(f, lseek(fileno(f), (off_t)0, SEEK_CUR), SEEK_SET);
+	{
+	    int saved_errno;
+	    off_t pos;
+
+	    saved_errno = errno;
+	    pos = lseek(fileno(f), (off_t)0, SEEK_CUR);
+	    if (pos != -1)
+		fseeko(f, pos, SEEK_SET);
+	    errno = saved_errno;
+	}
 #endif
         if (r == n) return len;
         if (0 <= r) {
@@ -1297,8 +1306,13 @@ io_getpartial(int argc, VALUE *argv, VAL
                 goto again;
             rb_sys_fail(fptr->path);
         }
-        if (fptr->f) /* update pos in FILE structure [ruby-core:21561] */
+        if (fptr->f) { /* update pos in FILE structure [ruby-core:21561] */
             fflush(fptr->f);
+#if defined(__SOFF) && defined(__NetBSD__)
+	    fptr->f->_flags &= ~__SOFF;
+	    (void)io_tell(fptr);
+#endif
+	}
     }
     rb_str_resize(str, n);