diff --git a/rpn b/rpn
index 70606be..268cc8f 100755
--- a/rpn
+++ b/rpn
@@ -10,7 +10,7 @@ my $stack_color = 'blue';
 print color $input_color;
 while (<>) {
     for (split) {
-	if (m{^[-+*/]|\*\*$}) {
+	if (m{^[-+*/%]|\*\*$}) {
 	    my $y = pop @stack;
 	    my $x = pop @stack;
 	    my $z = eval "$x $_ $y";