diff -ruN mopac7-1.15-orig/fortran/fdate.c mopac7-1.15/fortran/fdate.c
--- mopac7-1.15-orig/fortran/fdate.c	2008-08-21 10:05:23.000000000 -0500
+++ mopac7-1.15/fortran/fdate.c	2022-01-28 10:13:25.000000000 -0600
@@ -21,6 +21,12 @@
 #include <time.h>
 #include <string.h>
 
+#ifdef KR_headers
+VOID s_copy(a, b, la, lb) register char *a, *b; ftnlen la, lb;
+#else
+void s_copy(register char *a, register char *b, ftnlen la, ftnlen lb);
+#endif
+
 void fdate_(char *cht, ftnlen cht_len)
 {
     static time_t t;