Hallo, I've got a file open for IO. Only writing to it works okay. But if I also try to read from it, then things start going wrong. I've attached a test case that should return NIL but instead raises an error in ABCL (1.3.3, on OSX). The problem is with the call to #'write-sequence on line 21. In fact, from some other tests, I believe that replacing that call to #'write-sequence with a call to a function that does the same thing but by repeatedly setting the file-position and writing a byte, for each byte in the sequence, fixes things. That means something about #'write-sequence is broken. Maybe I misunderstand the file level functions in Common Lisp, and my test doesn't use them correctly. However, the test passes in: CLISP, CCL, CMUCL, SBCL, ECL. So I thought I'd report this, just in case it is a bug in ABCL. Also, removing the last three lines of code in #'main, which read one byte, makes the test run without errors. Vibhu