diff -U 3 -dHrN a/plan404/cmoon.c b/plan404/cmoon.c
--- a/plan404/cmoon.c	2024-11-09 10:33:59.000000000 +0100
+++ b/plan404/cmoon.c	2025-01-23 18:14:36.412869796 +0100
@@ -127,6 +127,7 @@
  */
 
 #include "plantbl.h"
+#include <math.h>
 
 extern int epsiln(double J);
 
@@ -551,7 +552,7 @@
 
 /* Beware of atan2()!
  */
-double floor(), sin(), cos(), asin(), mods3600();
+double mods3600(double);
 
 /* equatorial radius of the earth, in au
  */
@@ -560,7 +561,7 @@
 #define Kearth 6378.137
 
 extern double STR, DTR, J2000;
-int moon1(), moon2(), moon3(), moon4(), chewm(), sscc();
+int moon1(), moon2(), moon3(), moon4(int), chewm(short*,int,int,int,double*), sscc(int,double,int);
 
 
 #if AASUB
@@ -845,7 +846,6 @@
 double x;
 {
 double lx;
-double floor();
 
 lx = x;
 lx = lx - 1296000.0 * floor( lx/1296000.0 );
diff -U 3 -dHrN a/plan404/epsiln.c b/plan404/epsiln.c
--- a/plan404/epsiln.c	2024-11-09 10:33:59.000000000 +0100
+++ b/plan404/epsiln.c	2025-01-23 17:48:16.216078423 +0100
@@ -21,6 +21,7 @@
  * 
  */
  #include "plantbl.h"
+ #include <math.h>
 
 /* The results of the program are returned in these
  * global variables:
@@ -30,7 +31,6 @@
 double coseps = 0.0; /* Cosine of the obliquity */
 double sineps = 0.0; /* Sine of the obliquity */
 extern double eps, coseps, sineps, STR;
-double sin(), cos(), fabs();
 
 int epsiln(J)
 double J; /* Julian date input */
diff -U 3 -dHrN a/plan404/gplan.c b/plan404/gplan.c
--- a/plan404/gplan.c	2024-11-09 10:33:59.000000000 +0100
+++ b/plan404/gplan.c	2025-01-23 17:52:39.690327333 +0100
@@ -1,4 +1,5 @@
 #include "plantbl.h"
+#include <math.h>
 #define TIMESCALE 3652500.0
 #define mods3600(x) ((x) - 1.296e6 * floor ((x)/1.296e6))
 
@@ -43,8 +44,7 @@
 static double ss[9][24];
 static double cc[9][24];
 
-double cos (), sin (), floor (), fabs ();
-static int sscc ();
+static int sscc (int,double,int);
 
 int 
 gplan (J, plan, pobj)
diff -U 3 -dHrN a/plan404/nutate.c b/plan404/nutate.c
--- a/plan404/nutate.c	2024-11-09 10:33:59.000000000 +0100
+++ b/plan404/nutate.c	2025-01-23 18:07:43.080547973 +0100
@@ -21,6 +21,7 @@
  *                 tested against JPL DE403 ephemeris file.
  */
 #include "plantbl.h"
+#include <math.h>
 
 /* The answers are posted here by nutlo():
  */
@@ -173,9 +174,8 @@
 double ss[5][8];
 double cc[5][8];
 extern double ss[5][8], cc[5][8];
-int sscc(), epsiln(), showcor();
+int sscc(int,double,int), epsiln(double), showcor();
 
-double sin(), cos(), floor();
 #define mod3600(x) ((x) - 1296000. * floor ((x)/1296000.))
 
 int nutlo(J)
@@ -317,7 +317,6 @@
 double ce, se, cl, sl, sino, f;
 double dp[3], p1[3];
 int i;
-double sin(), cos();
 
 nutlo(J); /* be sure we calculated nutl and nuto */
 epsiln(J); /* and also the obliquity of date */
@@ -369,7 +368,6 @@
 {
 double cu, su, cv, sv, s;
 int i;
-double sin(), cos();
 
 su = sin(arg);
 cu = cos(arg);
diff -U 3 -dHrN a/plan404/plan404.c b/plan404/plan404.c
--- a/plan404/plan404.c	2024-11-09 10:33:59.000000000 +0100
+++ b/plan404/plan404.c	2025-01-23 17:55:19.459025255 +0100
@@ -34,6 +34,7 @@
 */
 
 #include <stdio.h>
+#include <math.h>
 #include "plantbl.h"
 #include "plan404.h"
 
@@ -53,11 +54,12 @@
   &plu404
 };
 
+typedef struct plantbl Plantbl;
+
 double sineps2k = 3.97777155754e-1; // ecliptic J2000
 double coseps2k = 9.17482062146e-1;
 
-double cos (), sin ();
-int gplan (), gmoon ();
+int gplan (double,Plantbl*,double*), gmoon (double,double*,double*);
 
 int Plan404 ( pla ) 
  struct PlanetData *pla;
diff -U 3 -dHrN a/plan404/precess.c b/plan404/precess.c
--- a/plan404/precess.c	2024-11-09 10:33:59.000000000 +0100
+++ b/plan404/precess.c	2025-01-23 18:04:20.687395388 +0100
@@ -3,6 +3,7 @@
  *
  * Program by Steve Moshier.  */
 #include "plantbl.h"
+#include <math.h>
 
 #define WILLIAMS 1
 /* James G. Williams, "Contributions to the Earth's obliquity rate,
@@ -62,13 +63,12 @@
  */
 
 #define DOUBLE double
-double cos(), sin();
 #define COS cos
 #define SIN sin
 extern DOUBLE J2000; /* = 2451545.0, 2000 January 1.5 */
 extern DOUBLE STR; /* = 4.8481368110953599359e-6 radians per arc second */
 extern DOUBLE coseps, sineps; /* see epsiln.c */
-extern int epsiln();
+extern int epsiln(double);
 
 /* In WILLIAMS and SIMON, Laskar's terms of order higher than t^4
    have been retained, because Simon et al mention that the solution
diff -U 3 -dHrN a/wcs/fitsfile.c b/wcs/fitsfile.c
--- a/wcs/fitsfile.c	2024-11-09 10:33:59.000000000 +0100
+++ b/wcs/fitsfile.c	2025-01-23 18:28:11.010552409 +0100
@@ -83,6 +83,7 @@
 #include <sys/file.h>
 #include <errno.h>
 #include <string.h>
+#include <strings.h>
 #include "fitsfile.h"
 
 static int verbose=0;		/* Print diagnostics */
diff -U 3 -dHrN a/wcs/imgetwcs.c b/wcs/imgetwcs.c
--- a/wcs/imgetwcs.c	2024-11-09 10:33:59.000000000 +0100
+++ b/wcs/imgetwcs.c	2025-01-23 18:42:54.560745332 +0100
@@ -31,6 +31,7 @@
 #include <stdlib.h>
 #include <math.h>
 #include <string.h>
+#include <strings.h>
 
 #include "wcs.h"
 #include "lwcs.h"
diff -U 3 -dHrN a/wcs/Makefile b/wcs/Makefile
--- a/wcs/Makefile	2025-01-23 17:23:42.116661645 +0100
+++ b/wcs/Makefile	2025-01-23 18:40:42.191867339 +0100
@@ -1,5 +1,5 @@
 # 
-CFLAGS= -w -fPIC $(arch_flags)
+CFLAGS= -w -fPIC $(arch_flags) -std=c17 -D_XOPEN_SOURCE=500
 OSTYPE = $(shell uname)
 ifneq ($(findstring BSD,$(OSTYPE)),)
 CC            = cc
diff -U 3 -dHrN a/wcs/wcscon.c b/wcs/wcscon.c
--- a/wcs/wcscon.c	2024-11-09 10:33:59.000000000 +0100
+++ b/wcs/wcscon.c	2025-01-23 18:42:59.588375118 +0100
@@ -71,6 +71,7 @@
 #include <stdio.h>	/* for fprintf() and sprintf() */
 #include <ctype.h>
 #include <string.h>
+#include <strings.h>
 #include "wcs.h"
 
 void fk524(), fk524e(), fk524m(), fk524pv();