diff --git a/lib/ipaddress.rb b/lib/ipaddress.rb
index 8b224312848bd8d32e94e3b2447b51f6bcc33a91..19b526f3cb1186e5308dc0cc39680caa600af4b0 100644
--- a/lib/ipaddress.rb
+++ b/lib/ipaddress.rb
@@ -214,7 +214,7 @@ end
 #
 # Compatibility with Ruby 1.8
 #
-if RUBY_VERSION =~ /1\.8/
+if RUBY_VERSION =~ /^1\.8/
   class Hash # :nodoc:
     alias :key :index
   end