diff --git a/Proxmox/Sys/Net.pm b/Proxmox/Sys/Net.pm
index 2d29116..c2f3e9c 100644
--- a/Proxmox/Sys/Net.pm
+++ b/Proxmox/Sys/Net.pm
@@ -7,7 +7,7 @@ use base qw(Exporter);
 our @EXPORT_OK = qw(parse_ip_address parse_ip_mask parse_fqdn);
 
 our $HOSTNAME_RE = "(?:[a-zA-Z0-9](?:[a-zA-Z0-9\-]{,61}?[a-zA-Z0-9])?)";
-our $FQDN_RE = "(?:${HOSTNAME_RE}\.)*${HOSTNAME_RE}";
+our $FQDN_RE = "(?:${HOSTNAME_RE}\\.)*${HOSTNAME_RE}";
 
 my $IPV4OCTET = "(?:25[0-5]|(?:2[0-4]|1[0-9]|[1-9])?[0-9])";
 my $IPV4RE = "(?:(?:$IPV4OCTET\\.){3}$IPV4OCTET)";
diff --git a/proxmox-installer-common/src/utils.rs b/proxmox-installer-common/src/utils.rs
index 0ed7438..ddfd7a1 100644
--- a/proxmox-installer-common/src/utils.rs
+++ b/proxmox-installer-common/src/utils.rs
@@ -309,6 +309,12 @@ mod tests {
             Fqdn::from(&format!("{}.com", "a".repeat(64))),
             Err(InvalidPart("a".repeat(64))),
         );
+
+        // https://bugzilla.proxmox.com/show_bug.cgi?id=5230
+        assert_eq!(
+            Fqdn::from("123@foo.com"),
+            Err(InvalidPart("123@foo".to_owned()))
+        );
     }
 
     #[test]
diff --git a/test/parse-fqdn.pl b/test/parse-fqdn.pl
index 3009984..6638fbe 100755
--- a/test/parse-fqdn.pl
+++ b/test/parse-fqdn.pl
@@ -51,4 +51,7 @@ is_parsed('a' x 63 . '.com', ['a' x 63, 'com']);
 is_invalid('a' x 250 . '.com', ERR_TOOLONG);
 is_invalid('a' x 64 . '.com', ERR_ALPHANUM);
 
+# https://bugzilla.proxmox.com/show_bug.cgi?id=5230
+is_invalid('123@foo.com', ERR_ALPHANUM);
+
 done_testing();