Index: Modules/_io/fileio.c
===================================================================
--- Modules/_io/fileio.c	(revision 75006)
+++ Modules/_io/fileio.c	(working copy)
@@ -47,7 +47,7 @@
 	int fd;
 	unsigned readable : 1;
 	unsigned writable : 1;
-	int seekable : 2; /* -1 means unknown */
+	signed int seekable : 2; /* -1 means unknown */
 	int closefd : 1;
 	PyObject *weakreflist;
 	PyObject *dict;