diff -burN tcsh-6.20.00.orig/config/linux tcsh-6.20.00/config/linux
--- tcsh-6.20.00.orig/config/linux	2011-02-05 19:14:20.000000000 +0300
+++ tcsh-6.20.00/config/linux	2017-07-20 16:32:08.471343251 +0300
@@ -86,6 +86,9 @@
  */
 
 #define __STRICT_ANSI__
+#ifndef _DEFAULT_SOURCE
+#define _DEFAULT_SOURCE
+#endif
 #ifndef _BSD_SOURCE
 # define _BSD_SOURCE
 #endif