diff --git a/README.md b/README.md
index 82db022..318b39c 100644
--- a/README.md
+++ b/README.md
@@ -49,6 +49,9 @@ Readonly - Facility for creating read-only scalars, arrays, hashes
     Readonly    \%has => (key => value, key => value, ...);
     Readonly \my %has => (key => value, key => value, ...);
 
+    # Some Perl style guides (Perl::Critic, PBP) recommend uppercase
+    Readonly my $PI => 4 * atan2 1, 1;
+
 # Description
 
 This is a facility for creating non-modifiable variables. This is useful for
diff --git a/lib/Readonly.pm b/lib/Readonly.pm
index a14ccc0..1eb0a23 100644
--- a/lib/Readonly.pm
+++ b/lib/Readonly.pm
@@ -500,6 +500,9 @@ Readonly - Facility for creating read-only scalars, arrays, hashes
     Readonly    \%has => (key => value, key => value, ...);
     Readonly \my %has => (key => value, key => value, ...);
 
+    # Some Perl style guides (Perl::Critic, PBP) recommend uppercase
+    Readonly my $PI => 4 * atan2 1, 1;
+
 =head1 Description
 
 This is a facility for creating non-modifiable variables. This is useful for