diff --git a/lib/PPI/Normal.pm b/lib/PPI/Normal.pm
index fd01413d..920dc533 100644
--- a/lib/PPI/Normal.pm
+++ b/lib/PPI/Normal.pm
@@ -86,7 +86,7 @@ sub register {
 		}
 
 		# Has it already been added?
-		if ( List::Util::any { $_ eq $function } ) {
+		if ( List::Util::any { $_ eq $function } map @{$_}, values %LAYER ) {
 			return 1;
 		}
 
diff --git a/t/09_normal.t b/t/09_normal.t
index 7f587b63..c5929110 100644
--- a/t/09_normal.t
+++ b/t/09_normal.t
@@ -59,6 +59,5 @@ NO_DOUBLE_REG: {
 	is $PPI::Normal::LAYER{2}[-1], "main::just_a_test_sub", "and find subs at right layer";
 	my $size = @{ $PPI::Normal::LAYER{2} };
 	ok( PPI::Normal->register( "main::just_a_test_sub", 2 ), "can add subs again" );
-	local $TODO = 'prevent duplicate registrations of normals';
 	is scalar @{ $PPI::Normal::LAYER{2} }, $size, "but sub isn't added twice";
 }