diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 98a7642..00610d3 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -11,7 +11,7 @@ jobs:
       - id: versions
         run: |
           versions=$(curl -s 'https://cache.ruby-lang.org/pub/misc/ci_versions/all.json' | jq -c '. + ["2.5"]')
-          echo "::set-output name=value::${versions}"
+          echo "value=${versions}" >> $GITHUB_OUTPUT
   test:
     needs: ruby-versions
     name: build (${{ matrix.ruby }} / ${{ matrix.os }})
diff --git a/lib/optparse.rb b/lib/optparse.rb
index dc2b8a0..53a4387 100644
--- a/lib/optparse.rb
+++ b/lib/optparse.rb
@@ -425,7 +425,7 @@
 # If you have any questions, file a ticket at http://bugs.ruby-lang.org.
 #
 class OptionParser
-  OptionParser::Version = "0.3.0"
+  OptionParser::Version = "0.3.1"
 
   # :stopdoc:
   NoArgument = [NO_ARGUMENT = :NONE, nil].freeze
@@ -2084,10 +2084,23 @@ def environment(env = File.basename($0, '.*'))
       f |= Regexp::IGNORECASE if /i/ =~ o
       f |= Regexp::MULTILINE if /m/ =~ o
       f |= Regexp::EXTENDED if /x/ =~ o
-      k = o.delete("imx")
-      k = nil if k.empty?
+      case o = o.delete("imx")
+      when ""
+      when "u"
+        s = s.encode(Encoding::UTF_8)
+      when "e"
+        s = s.encode(Encoding::EUC_JP)
+      when "s"
+        s = s.encode(Encoding::SJIS)
+      when "n"
+        f |= Regexp::NOENCODING
+      else
+        raise OptionParser::InvalidArgument, "unknown regexp option - #{o}"
+      end
+    else
+      s ||= all
     end
-    Regexp.new(s || all, f, k)
+    Regexp.new(s, f)
   end
 
   #
diff --git a/test/optparse/test_optparse.rb b/test/optparse/test_optparse.rb
index 5a0593d..bfa705a 100644
--- a/test/optparse/test_optparse.rb
+++ b/test/optparse/test_optparse.rb
@@ -63,6 +63,9 @@ def test_regexp
     assert_equal(/foo/i, @reopt)
     assert_equal(%w"", no_error {@opt.parse!(%w"--regexp=/foo/n")})
     assert_equal(/foo/n, @reopt)
+    assert_equal(%w"", no_error {@opt.parse!(%W"--regexp=/\u{3042}/s")})
+    assert_equal(Encoding::Windows_31J, @reopt.encoding)
+    assert_equal("\x82\xa0".force_encoding(Encoding::Windows_31J), @reopt.source)
   end
 
   def test_into