diff --git a/lib/fimg-pnm.c b/lib/fimg-pnm.c
index b642ef8..80db3e6 100644
--- a/lib/fimg-pnm.c
+++ b/lib/fimg-pnm.c
@@ -165,7 +165,7 @@ fprintf(fp, "%s\n%d %d\n", code, head->width, head->height);
 
 maximum = fimg_get_maxvalue(head);
 fprintf(fp, "#  maxval  %15f\n", maximum);
-fk = maximum / 65536.0;
+fk = maximum / 65535.0;
 fprintf(fp, "# divisor  %15f\n", fk);
 fprintf(fp, "65535\n");
 fflush(fp);