diff --git a/lib/Syntax/Construct.pm b/lib/Syntax/Construct.pm
index 4b449a0..933c7f5 100644
--- a/lib/Syntax/Construct.pm
+++ b/lib/Syntax/Construct.pm
@@ -201,8 +201,12 @@ sub _hook {
           eval {
               use locale;
               require POSIX;
-              POSIX::setlocale(POSIX::LC_ALL(), 'tr_TR.UTF-8');
-              lc 'I' ne 'i'
+              my $orig_locale = POSIX::setlocale(POSIX::LC_CTYPE());
+              POSIX::setlocale(POSIX::LC_CTYPE(), 'tr_TR.UTF-8')
+                  eq 'tr_TR.UTF-8' or die;
+              my $cmp = lc 'I' ne 'i';
+              POSIX::setlocale(POSIX::LC_CTYPE(), $orig_locale);
+              $cmp
           } or die 'Turkic locale casing not working at '
               . _position(1) . "\.\n";
       },
diff --git a/t/02-constructs.t b/t/02-constructs.t
index 3d79a3c..7161f0b 100755
--- a/t/02-constructs.t
+++ b/t/02-constructs.t
@@ -115,8 +115,12 @@ my %tests = (
           q("\N{ORIYA DIGIT FOUR}" =~ m'\N{ORIYA DIGIT FOUR}'), 1 ],
         [ 'turkic-casing',
           'use locale; use POSIX "locale_h";' . skippable(
-              'eval{setlocale(LC_ALL, "tr_TR.UTF-8") eq "tr_TR.UTF-8" or die;'
-                  . ' lc "I" eq "\N{LATIN SMALL LETTER DOTLESS I}"}',
+              'my $o = setlocale(LC_CTYPE);'
+              . 'eval {'
+              .    'setlocale(LC_CTYPE, "tr_TR.UTF-8") eq "tr_TR.UTF-8" or die;'
+              .    'my $r = lc "I" eq "\N{LATIN SMALL LETTER DOTLESS I}";'
+              .    'setlocale(LC_CTYPE, $o);'
+              . '$r }',
               '": testing locale not supported"',
               "", '1'),
           1 ],