--- at-3.1.16/parsetime.orig.y
+++ at-3.1.16/parsetime.y
@@ -17,6 +17,9 @@
 extern int yylex();
 
 int add_date(int number, int period);
+#ifndef __isleap
+#define __isleap(year) ((year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0))
+#endif
 %}
 
 %union {