diff --git a/src/ChangeLog b/src/ChangeLog
index 9ee108ba..c32550ec 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,7 @@
+2003-11-08  Hrvoje Niksic  <hniksic@xemacs.org>
+
+	* connect.c (register_extended): Check that fd >= 0.
+
 2003-11-07  Hrvoje Niksic  <hniksic@xemacs.org>
 
 	* connect.c (LAZY_RETRIEVE_INFO): Set LAST_INFO.
diff --git a/src/connect.c b/src/connect.c
index c835fa92..a88e2595 100644
--- a/src/connect.c
+++ b/src/connect.c
@@ -628,7 +628,14 @@ void
 register_extended (int fd, xreader_t reader, xwriter_t writer,
 		   xpoller_t poller, xcloser_t closer, void *ctx)
 {
-  struct extended_info *info = xnew (struct extended_info);
+  struct extended_info *info;
+
+  /* The file descriptor must be non-negative to be registered.
+     Negative values are ignored by xclose(), and -1 cannot be used as
+     hash key.  */
+  assert (fd >= 0);
+
+  info = xnew (struct extended_info);
   info->reader = reader;
   info->writer = writer;
   info->poller = poller;