[perl #68640] Wrong error for undef constant name

2 files changed, 12 insertions, 7 deletions

diff --git a/dist/constant/lib/constant.pm b/dist/constant/lib/constant.pm
index a51ee7f277..3ee1a6f5b0 100644
--- a/dist/constant/lib/constant.pm
+++ b/dist/constant/lib/constant.pm
@@ -4,7 +4,7 @@ use strict;
 use warnings::register;
 
 use vars qw($VERSION %declared);
-$VERSION = '1.19';
+$VERSION = '1.20';
 
 #=======================================================================
 
@@ -60,15 +60,14 @@ sub import {
 	}
 	$constants = shift;
     } else {
-	$constants->{+shift} = undef;
-    }
-
-    foreach my $name ( keys %$constants ) {
-	unless (defined $name) {
+	unless (defined $_[0]) {
 	    require Carp;
 	    Carp::croak("Can't use undef as constant name");
 	}
+	$constants->{+shift} = undef;
+    }
 
+    foreach my $name ( keys %$constants ) {
 	# Normal constant name
 	if ($name =~ $normal_constant_name and !$forbidden{$name}) {
 	    # Everything is okay
diff --git a/dist/constant/t/constant.t b/dist/constant/t/constant.t
index a42b7d2281..85a9355a19 100644
--- a/dist/constant/t/constant.t
+++ b/dist/constant/t/constant.t
@@ -9,7 +9,7 @@ END { @warnings && print STDERR join "\n- ", "accumulated warnings:", @warnings
 
 
 use strict;
-use Test::More tests => 95;
+use Test::More tests => 96;
 my $TB = Test::More->builder;
 
 BEGIN { use_ok('constant'); }
@@ -341,3 +341,9 @@ $kloong = 'schlozhauer';
     is ($@, '');
     is_deeply (\@value, []);
 }
+
+{
+    local $SIG{'__WARN__'} = sub { die "WARNING: $_[0]" };
+    eval 'use constant undef, 5; 1';
+    like $@, qr/\ACan't use undef as constant name at /;
+}