diff --git a/liolib.c b/liolib.c
index f61e1823..95b74795 100644
--- a/liolib.c
+++ b/liolib.c
@@ -1,5 +1,5 @@
 /*
-** $Id: liolib.c,v 2.28 2002/12/04 17:38:31 roberto Exp roberto $
+** $Id: liolib.c,v 2.29 2002/12/20 10:26:33 roberto Exp roberto $
 ** Standard I/O (and system) library
 ** See Copyright Notice in lua.h
 */
@@ -28,6 +28,13 @@
 */
 
 
+#ifdef _POSIX_C_SOURCE
+#if _POSIX_C_SOURCE >= 2
+#define USE_POPEN
+#endif
+#endif
+
+
 #ifndef USE_POPEN
 #define pclose(f)    (-1)
 #endif
diff --git a/lua.c b/lua.c
index 1f303d20..8ae2607a 100644
--- a/lua.c
+++ b/lua.c
@@ -1,5 +1,5 @@
 /*
-** $Id: lua.c,v 1.112 2002/12/04 17:28:27 roberto Exp roberto $
+** $Id: lua.c,v 1.113 2002/12/04 17:38:31 roberto Exp roberto $
 ** Lua stand-alone interpreter
 ** See Copyright Notice in lua.h
 */
@@ -26,7 +26,7 @@
 #endif
 
 
-#ifdef _POSIX_SOURCE
+#ifdef _POSIX_C_SOURCE
 #include <unistd.h>
 #else
 static int isatty (int x) { return x==0; }  /* assume stdin is a tty */