diff --git a/unix/m4/glibc2.m4 b/unix/m4/glibc2.m4
new file mode 100644
index 0000000..e8f5bfe
--- /dev/null
+++ b/unix/m4/glibc2.m4
@@ -0,0 +1,30 @@
+# glibc2.m4 serial 1
+dnl Copyright (C) 2000-2002, 2004 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+# Test for the GNU C Library, version 2.0 or newer.
+# From Bruno Haible.
+
+AC_DEFUN([gt_GLIBC2],
+  [
+    AC_CACHE_CHECK(whether we are using the GNU C Library 2 or newer,
+      ac_cv_gnu_library_2,
+      [AC_EGREP_CPP([Lucky GNU user],
+	[
+#include <features.h>
+#ifdef __GNU_LIBRARY__
+ #if (__GLIBC__ >= 2)
+  Lucky GNU user
+ #endif
+#endif
+	],
+	ac_cv_gnu_library_2=yes,
+	ac_cv_gnu_library_2=no)
+      ]
+    )
+    AC_SUBST(GLIBC2)
+    GLIBC2="$ac_cv_gnu_library_2"
+  ]
+)