--- gdb/ser-base.c	(revision 3592)
+++ gdb/ser-base.c	(local)
@@ -361,6 +361,9 @@ generic_readchar (struct serial *scb, in
 	  if (num_bytes != -1)
 	    to_read = (num_bytes < to_read) ? num_bytes : to_read;
 
+	  if (to_read == 0)
+	    break;
+
 	  s = read (scb->error_fd, &buf, to_read);
 	  if (s == -1)
 	    break;
--- gdb/ser-mingw.c	(revision 3592)
+++ gdb/ser-mingw.c	(local)
@@ -875,7 +875,7 @@ pipe_done_wait_handle (struct serial *sc
 static int
 pipe_avail (struct serial *scb, int fd)
 {
-  HANDLE h = (HANDLE) _get_osfhandle (scb->error_fd);
+  HANDLE h = (HANDLE) _get_osfhandle (fd);
   DWORD numBytes;
   BOOL r = PeekNamedPipe (h, NULL, 0, NULL, &numBytes, NULL);
   if (r == FALSE)
--- gdb/serial.h	(revision 3592)
+++ gdb/serial.h	(local)
@@ -255,7 +255,7 @@ struct serial_ops
        without blocking.  Return value of -1 means that the
        the read will not block even if less that requested bytes
        are available.  */
-    int (*avail)(struct serial *scb);
+    int (*avail)(struct serial *scb, int fd);
 
 #ifdef USE_WIN32API
     /* Return a handle to wait on, indicating available data from SCB