--- a/util-src/pposix.c	Fri Nov 22 15:27:21 2013 +0100
+++ b/util-src/pposix.c	Thu Nov 28 16:12:40 2013 +0100
@@ -666,6 +666,8 @@
 {
 	off_t offset, len;
 	FILE *f = *(FILE**) luaL_checkudata(L, 1, LUA_FILEHANDLE);
+	if (f == NULL)
+		luaL_error(L, "attempt to use a closed file");
 
 	offset = luaL_checkinteger(L, 2);
 	len = luaL_checkinteger(L, 3);