diff --git a/lib/tmpdir.rb b/lib/tmpdir.rb
index 962393f98a..6e47ac4fc7 100644
--- a/lib/tmpdir.rb
+++ b/lib/tmpdir.rb
@@ -121,7 +121,7 @@ class Dir
 
     # Dedicated random number generator
     RANDOM = Random.new
-    class << Random # :nodoc:
+    class << RANDOM # :nodoc:
       # Maximum random number
       MAX = 36**6 # < 0x100000000