diff --git a/lib/Email/Address.pm b/lib/Email/Address.pm
index f642b77..7fe1deb 100644
--- a/lib/Email/Address.pm
+++ b/lib/Email/Address.pm
@@ -54,7 +54,11 @@ my $cfws           = qr/$comment|(?>\s+)/;
 my $atext          = qq/[^$CTL$special\\s]/;
 my $atom           = qr/(?>$cfws*$atext+$cfws*)/;
 my $dot_atom_text  = qr/(?>$atext+(?:\.$atext+)*)/;
+my $fqdn_atom_text = qr/(?>$atext+\.$atext+(?:\.$atext+)*)/;  # Requires at least one dot
+my $localhost_text = qr/localhost/i;
 my $dot_atom       = qr/(?>$cfws*$dot_atom_text$cfws*)/;
+my $fqdn_atom      = qr/(?>$cfws*$fqdn_atom_text$cfws*)/;
+my $localhost_atom = qr/(?>$cfws*$localhost_text$cfws*)/;
 
 my $qtext          = qr/[^\\"]/;
 my $qcontent       = qr/$qtext|$quoted_pair/;
@@ -83,7 +87,7 @@ my $local_part     = qr/$dot_atom|$quoted_string/;
 my $dtext          = qr/[^\[\]\\]/;
 my $dcontent       = qr/$dtext|$quoted_pair/;
 my $domain_literal = qr/(?>$cfws*\[(?:\s*$dcontent)*\s*\]$cfws*)/;
-my $domain         = qr/$dot_atom|$domain_literal/;
+my $domain         = qr/$fqdn_atom|$localhost_atom|$domain_literal/;
 
 my $display_name   = $phrase;
 
diff --git a/t/rfc5322-compliance.t b/t/rfc5322-compliance.t
new file mode 100755
index 0000000..4119f16
--- /dev/null
+++ b/t/rfc5322-compliance.t
@@ -0,0 +1,50 @@
+#!/usr/bin/env perl
+use strict;
+use warnings;
+use Test::More;
+use Email::Address;
+
+# Regression test for RFC 5322 compliance issue found in Koha
+# Email::Address should reject addresses without proper TLD per RFC 5322
+
+# Test addresses that should be INVALID (missing TLD)
+my @invalid_addresses = (
+    'test@gmail',
+    'admin@server',
+    'user@domain',
+);
+
+# Test addresses that should be VALID (proper FQDN)
+my @valid_addresses = (
+    'test@gmail.com',
+    'user@localhost',  # localhost is a special case that may be valid
+    'admin@server.example.com',
+);
+
+# Test that invalid addresses are rejected
+for my $addr (@invalid_addresses) {
+    my @parsed = Email::Address->parse($addr);
+    is(scalar(@parsed), 0, "$addr should be rejected (missing TLD)");
+}
+
+# Test that valid addresses are accepted
+for my $addr (@valid_addresses) {
+    my @parsed = Email::Address->parse($addr);
+    is(scalar(@parsed), 1, "$addr should be accepted (valid FQDN)");
+}
+
+done_testing();
+
+__END__
+
+=head1 NAME
+
+rfc5322-compliance.t - Regression test for RFC 5322 compliance
+
+=head1 DESCRIPTION
+
+This test ensures Email::Address properly rejects email addresses that violate
+RFC 5322 by lacking fully qualified domain names (FQDN).
+
+Currently FAILS because Email::Address incorrectly accepts addresses like
+'test@gmail' when they should be rejected per RFC 5322.