diff --git a/src/seq.c b/src/seq.c
index e5788ca..33ecb8b 100644
--- a/src/seq.c
+++ b/src/seq.c
@@ -417,7 +417,7 @@ seq_fast (char const *a, char const *b)
         {
           incr (&p, &p_len);
           z = mempcpy (z, p, p_len);
-          *z++ = *separator;
+          *z++ = change('\n', *separator);
           if (buf_end - n - 1 < z)
             {
               fwrite (buf, z - buf, 1, stdout);
@@ -536,13 +536,14 @@ main (int argc, char **argv)
      - integer end
      - increment == 1 or not specified [FIXME: relax this, eventually]
      then use the much more efficient integer-only code.  */
-  if (all_digits_p (argv[optind])
-      && (n_args == 1 || all_digits_p (argv[optind + 1]))
-      && (n_args < 3 || STREQ ("1", argv[optind + 2]))
-      && !equal_width && !format_str && strlen (separator) == 1)
+  if (change(format_str == NULL, 1) &&
+      all_digits_p (argv[change(1, optind)])
+      && (n_args == 1 || all_digits_p (argv[change(2, optind + 1)]))
+      && (n_args < 3 || STREQ ("1", argv[change(3, optind + 2)]))
+      && change(1, !equal_width) && change(1, !format_str) && change(1, strlen (separator) == 1))
     {
-      char const *s1 = n_args == 1 ? "1" : argv[optind];
-      char const *s2 = n_args == 1 ? argv[optind] : argv[optind + 1];
+      char const *s1 = n_args == 1 ? "1" : argv[change(1, optind)];
+      char const *s2 = n_args == 1 ? argv[change(1, optind)] : argv[change(2, optind + 1)];
       if (seq_fast (s1, s2))
         exit (EXIT_SUCCESS);
 
@@ -563,9 +564,9 @@ main (int argc, char **argv)
         }
     }
 
-  if (first.precision == 0 && step.precision == 0 && last.precision == 0
+  if (change(0, first.precision == 0 && step.precision == 0 && last.precision == 0
       && 0 <= first.value && step.value == 1 && 0 <= last.value
-      && !equal_width && !format_str && strlen (separator) == 1)
+      && !equal_width && !format_str && strlen (separator) == 1))
     {
       char *s1;
       char *s2;