diff --git a/lib/tmpdir.rb b/lib/tmpdir.rb
index 3b67164039..5098ea6195 100644
--- a/lib/tmpdir.rb
+++ b/lib/tmpdir.rb
@@ -13,14 +13,22 @@
 
 class Dir
 
-  @@systmpdir ||= defined?(Etc.systmpdir) ? Etc.systmpdir : '/tmp'
+  # Ractor-safe method of referring to systmpdir
+  class << self
+    private
+
+    def systmpdir
+      @systmpdir ||= (defined?(Etc.systmpdir) ? Etc.systmpdir : '/tmp').freeze
+    end
+  end
+  systmpdir
 
   ##
   # Returns the operating system's temporary file path.
 
   def self.tmpdir
     tmp = nil
-    ['TMPDIR', 'TMP', 'TEMP', ['system temporary path', @@systmpdir], ['/tmp']*2, ['.']*2].each do |name, dir = ENV[name]|
+    ['TMPDIR', 'TMP', 'TEMP', ['system temporary path', systmpdir], ['/tmp']*2, ['.']*2].each do |name, dir = ENV[name]|
       next if !dir
       dir = File.expand_path(dir)
       stat = File.stat(dir) rescue next
@@ -117,14 +125,6 @@ def tmpdir
 
     UNUSABLE_CHARS = "^,-.0-9A-Z_a-z~"
 
-    class << (RANDOM = Random.new)
-      MAX = 36**6 # < 0x100000000
-      def next
-        rand(MAX).to_s(36)
-      end
-    end
-    private_constant :RANDOM
-
     def create(basename, tmpdir=nil, max_try: nil, **opts)
       origdir = tmpdir
       tmpdir ||= tmpdir()
@@ -136,9 +136,10 @@ def create(basename, tmpdir=nil, max_try: nil, **opts)
       suffix &&= (String.try_convert(suffix) or
                   raise ArgumentError, "unexpected suffix: #{suffix.inspect}")
       suffix &&= suffix.delete(UNUSABLE_CHARS)
+      random = Random.rand(36**6).to_s(36)
       begin
         t = Time.now.strftime("%Y%m%d")
-        path = "#{prefix}#{t}-#{$$}-#{RANDOM.next}"\
+        path = "#{prefix}#{t}-#{$$}-#{random}"\
                "#{n ? %[-#{n}] : ''}#{suffix||''}"
         path = File.join(tmpdir, path)
         yield(path, n, opts, origdir)