diff --git a/lib/tempfile.rb b/lib/tempfile.rb
index 0d3c2a3901..64441511fe 100644
--- a/lib/tempfile.rb
+++ b/lib/tempfile.rb
@@ -122,7 +122,7 @@ class Tempfile < DelegateClass(File)
   #
   # If Tempfile.new cannot find a unique filename within a limited
   # number of tries, then it will raise an exception.
-  def initialize(basename, tmpdir=nil, mode: 0, **opts)
+  def initialize(basename, tmpdir=nil, mode: 0, **options)
     if block_given?
       warn "Tempfile.new doesn't call the given block."
     end
@@ -130,7 +130,7 @@ class Tempfile < DelegateClass(File)
     @clean_proc = Remover.new(@data)
     ObjectSpace.define_finalizer(self, @clean_proc)
 
-    ::Dir::Tmpname.create(basename, tmpdir, opts) do |tmpname, n, opts|
+    ::Dir::Tmpname.create(basename, tmpdir, options) do |tmpname, n, opts|
       mode |= File::RDWR|File::CREAT|File::EXCL
       opts[:perm] = 0600
       @data[1] = @tmpfile = File.open(tmpname, mode, opts)
@@ -347,9 +347,9 @@ end
 #      ... do something with f ...
 #   end
 #
-def Tempfile.create(basename, tmpdir=nil, mode: 0, **opts)
+def Tempfile.create(basename, tmpdir=nil, mode: 0, **options)
   tmpfile = nil
-  Dir::Tmpname.create(basename, tmpdir, opts) do |tmpname, n, opts|
+  Dir::Tmpname.create(basename, tmpdir, options) do |tmpname, n, opts|
     mode |= File::RDWR|File::CREAT|File::EXCL
     opts[:perm] = 0600
     tmpfile = File.open(tmpname, mode, opts)
diff --git a/lib/tmpdir.rb b/lib/tmpdir.rb
index 0b21f00d8e..7bd99e1fbb 100644
--- a/lib/tmpdir.rb
+++ b/lib/tmpdir.rb
@@ -105,21 +105,12 @@ class Dir
       Dir.tmpdir
     end
 
-    def make_tmpname(prefix_suffix, n)
-      case prefix_suffix
-      when String
-        prefix = prefix_suffix
-        suffix = ""
-      when Array
-        prefix = prefix_suffix[0]
-        suffix = prefix_suffix[1]
-      else
-        raise ArgumentError, "unexpected prefix_suffix: #{prefix_suffix.inspect}"
-      end
+    def make_tmpname((prefix, suffix), n)
       t = Time.now.strftime("%Y%m%d")
       path = "#{prefix}#{t}-#{$$}-#{rand(0x100000000).to_s(36)}"
       path << "-#{n}" if n
-      path << suffix
+      path << suffix if suffix
+      path
     end
 
     def create(basename, tmpdir=nil, max_try: nil, **opts)
diff --git a/test/test_tempfile.rb b/test/test_tempfile.rb
index 61457e4138..eb61120b69 100644
--- a/test/test_tempfile.rb
+++ b/test/test_tempfile.rb
@@ -1,5 +1,6 @@
 require 'test/unit'
 require 'tempfile'
+require 'thread'
 require_relative 'ruby/envutil'
 
 class TestTempfile < Test::Unit::TestCase