diff --git a/lib/tmpdir.rb b/lib/tmpdir.rb
index 55920a4..9f8f6b0 100644
--- a/lib/tmpdir.rb
+++ b/lib/tmpdir.rb
@@ -19,10 +19,11 @@ class Dir
   # Returns the operating system's temporary file path.
 
   def self.tmpdir
-    ['TMPDIR', 'TMP', 'TEMP', ['system temporary path', @@systmpdir], ['/tmp']*2, ['.']*2].find do |name, dir|
-      unless dir
-        next if !(dir = ENV[name]) or dir.empty?
-      end
+    candidate_dirs = ['TMPDIR', 'TMP', 'TEMP'].map(&ENV.method(:[]))
+    fallback_dirs = [@@systmpdir, '/tmp', '.']
+
+    (candidate_dirs + fallback_dirs).find do |dir|
+      next if !dir or dir.empty?
       dir = File.expand_path(dir)
       stat = File.stat(dir) rescue next
       case