diff -rup a/hijri/src/demo_hijri.c b/hijri/src/demo_hijri.c
--- a/hijri/src/demo_hijri.c	2009-03-08 17:55:11.000000000 -0400
+++ b/hijri/src/demo_hijri.c	2023-02-15 16:10:43.759285213 -0500
@@ -23,6 +23,7 @@
  ************************************************************************/
 
 #include <stdio.h>
+#include <stdlib.h>
 #include <time.h>               /* for time_t */
 #include "hijri.h"
 
diff -rup a/hijri/src/hijri.c b/hijri/src/hijri.c
--- a/hijri/src/hijri.c	2009-03-08 17:55:22.000000000 -0400
+++ b/hijri/src/hijri.c	2023-02-15 14:47:03.794285625 -0500
@@ -109,6 +109,10 @@ char *h_month_short[13] = {"skip",
 			   "Ram", "Sha", "Qid", "Hij"};
 
 
+/* Forward declarations for C99 compatibility.  */
+int g_absolute(int day, int month, int year);
+int g_numdays(int month, int year);
+
 /* Store-off any events for passed-in date */
 int
 get_events(char ***addr_event,
diff -rup a/hijri/src/umm_alqura.c b/hijri/src/umm_alqura.c
--- a/hijri/src/umm_alqura.c	2009-03-08 17:55:45.000000000 -0400
+++ b/hijri/src/umm_alqura.c	2023-02-15 16:08:27.002858747 -0500
@@ -81,6 +81,11 @@ double ip(double x);
 int mod(double x, double y);
 int IsValid(int yh, int mh, int dh);
 
+int fill_datestruct(sDate *fdate, int weekday, int frm_month_num,
+		    int to_month_num, char *frm_day[], char *frm_day_short[],
+		    char *frm_month[], char *frm_month_short[], char *to_day[],
+		    char *to_day_short[], char *to_month[],
+		    char *to_month_short[], sEvent *farr_table, int farr_size);
 
 /****************************************************************************/
 /* Name:    Hsub2G                                                          */