diff --git a/lib/LWP/UserAgent.pm b/lib/LWP/UserAgent.pm
index 64dcde5..e538e8e 100644
--- a/lib/LWP/UserAgent.pm
+++ b/lib/LWP/UserAgent.pm
@@ -1059,7 +1059,7 @@ sub proxy {
         my $url = shift;
         if (defined($url) && length($url)) {
             Carp::croak("Proxy must be specified as absolute URI; '$url' is not") unless $url =~ /^$URI::scheme_re:/;
-            Carp::croak("Bad http proxy specification '$url'") if $url =~ /^https?:/ && $url !~ m,^https?://(?:\w|\[),;
+            Carp::croak("Bad http proxy specification '$url'") if $url =~ /^https?:/ && $url !~ m,^https?://\w,;
         }
         $self->{proxy}{$key} = $url;
         $self->set_my_handler("request_preprepare", \&_need_proxy)