#!/usr/bin/env perl

use strict;
use warnings;

use Test::More;

use File::Temp;

my $mask;
my @fhs;

while (!defined $mask) {
    push @fhs, scalar File::Temp::tempfile();
    vec( my $curmask, fileno($fhs[-1]), 1 ) = 1;

    if ($curmask =~ m<[\x80-\xff]>) {
        $mask = $curmask;
    }
}

print "FD: " . fileno($fhs[-1]) . $/;

my $result = select $mask, undef, undef, 0;
print "error: $!" if $result == -1;

is($result, 1, 'file is readable (downgraded input to select)');

utf8::upgrade($mask);

$result = select $mask, undef, undef, 0;

is($result, 1, 'file is readable (upgraded input to select)');

done_testing;

diff --git a/pp_sys.c b/pp_sys.c
index a3bc0794a2..6bfa98f14f 100644
--- a/pp_sys.c
+++ b/pp_sys.c
@@ -1165,7 +1165,10 @@ PP(pp_sselect)
                 Perl_croak_no_modify();
         }
         else if (SvIsCOW(sv)) sv_force_normal_flags(sv, 0);
-        if (!SvPOK(sv)) {
+        if (SvPOK(sv)) {
+            if (SvUTF8(sv)) sv_utf8_downgrade(sv, FALSE);
+        }
+        else {
             if (!SvPOKp(sv))
                 Perl_ck_warner(aTHX_ packWARN(WARN_MISC),
                                     "Non-string passed as bitmask");