--- OLD/ppm/libppm5.c	Thu Jan  1 00:00:00 1970
+++ NEW/ppm/libppm5.c	Thu Jan  1 00:00:00 1970
@@ -546,12 +546,11 @@
     ++(fh->n);
     }
 
-static int yx_compare ARGS((coord* c1, coord* c2));
-static int
-yx_compare( c1, c2 )
-    coord* c1;
-    coord* c2;
+static int yx_compare ARGS((const void *, const void *));
+static int yx_compare(const void *c1v, const void *c2v)
     {
+    const coord *c1 = c1v;
+    const coord *c2 = c2v;
     if ( c1->y > c2->y )
 	return 1;
     if ( c1->y < c2->y )