diff --git a/activesupport/lib/active_support/core_ext/string/conversions.rb b/activesupport/lib/active_support/core_ext/string/conversions.rb
index af277f999517a044d9d81e95678da41a35c10a16..857ecfaa54dc8601f7db709b09f02eb9d9062008 100644
--- a/activesupport/lib/active_support/core_ext/string/conversions.rb
+++ b/activesupport/lib/active_support/core_ext/string/conversions.rb
@@ -30,7 +30,7 @@ def ord
 
   def getbyte(index)
     self[index]
-  end if RUBY_VERSION < '1.9'
+  end unless method_defined?(:getbyte)
 
   # Form can be either :utc (default) or :local.
   def to_time(form = :utc)