diff --git a/ChangeLog b/ChangeLog
index b96cacae4d..3a4e2281f6 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+Mon Jun 20 02:38:29 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* lib/optparse.rb (OptionParser::Completion.candidate): get rid of
+	  nil as key names.  [ruby-core:75773] [Bug #12438]
+
+	* lib/optparse.rb (OptionParser#make_switch): char class option
+	  cannot be NoArgument, default to RequiredArgument.
+
 Mon Jun 20 02:25:44 2016  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* re.c (unescape_nonascii): scan hex up to only 3 characters.
diff --git a/lib/optparse.rb b/lib/optparse.rb
index 3db7d757bd..74d7e8c67c 100644
--- a/lib/optparse.rb
+++ b/lib/optparse.rb
@@ -413,7 +413,7 @@ class OptionParser
       candidates = []
       block.call do |k, *v|
         (if Regexp === k
-           kn = nil
+           kn = "".freeze
            k === key
          else
            kn = defined?(k.id2name) ? k.id2name : k
@@ -1336,6 +1336,7 @@ XXX
     default_pattern = nil
     klass = nil
     q, a = nil
+    has_arg = false
 
     opts.each do |o|
       # argument class
@@ -1414,6 +1415,8 @@ XXX
         if a
           default_style = default_style.guess(arg = a)
           default_pattern, conv = search(:atype, o) unless default_pattern
+        else
+          has_arg = true
         end
         sdesc << "-#{q}"
         short << Regexp.new(q)
@@ -1436,6 +1439,9 @@ XXX
 
     default_pattern, conv = search(:atype, default_style.pattern) unless default_pattern
     if !(short.empty? and long.empty?)
+      if has_arg and default_style == Switch::NoArgument
+        default_style = Switch::RequiredArgument
+      end
       s = (style || default_style).new(pattern || default_pattern,
                                        conv, sdesc, ldesc, arg, desc, block)
     elsif !block
diff --git a/test/optparse/test_cclass.rb b/test/optparse/test_cclass.rb
new file mode 100644
index 0000000000..ac46f46bb2
--- /dev/null
+++ b/test/optparse/test_cclass.rb
@@ -0,0 +1,18 @@
+# frozen_string_literal: false
+require_relative 'test_optparse'
+
+class TestOptionParser::CClass < TestOptionParser
+  def test_no_argument
+    flags = []
+    @opt.def_option("-[a-z]") {|x| flags << x}
+    no_error {@opt.parse!(%w"-a")}
+    assert_equal(%w"a", flags)
+  end
+
+  def test_required_argument
+    flags = []
+    @opt.def_option("-[a-z]X") {|x| flags << x}
+    no_error {@opt.parse!(%w"-a")}
+    assert_equal(%w"a", flags)
+  end
+end
diff --git a/version.h b/version.h
index 93f4c65374..9643b4b662 100644
--- a/version.h
+++ b/version.h
@@ -1,6 +1,6 @@
 #define RUBY_VERSION "2.3.2"
 #define RUBY_RELEASE_DATE "2016-06-20"
-#define RUBY_PATCHLEVEL 134
+#define RUBY_PATCHLEVEL 135
 
 #define RUBY_RELEASE_YEAR 2016
 #define RUBY_RELEASE_MONTH 6