diff --git a/mrblib/float.rb b/mrblib/float.rb
index 6343b9b85..2b86dc1e5 100644
--- a/mrblib/float.rb
+++ b/mrblib/float.rb
@@ -6,4 +6,4 @@ class Float
   # mruby special - since mruby integers may be upgraded to floats,
   # floats should be compatible to integers.
   include Integral
-end
+end if class_defined?("Float")