1 files changed, 5 insertions, 1 deletions
diff --git a/activesupport/lib/active_support/core_ext/object/inclusion.rb b/activesupport/lib/active_support/core_ext/object/inclusion.rb
index cc7edc0f17..b5671f66d0 100644
--- a/activesupport/lib/active_support/core_ext/object/inclusion.rb
+++ b/activesupport/lib/active_support/core_ext/object/inclusion.rb
@@ -1,11 +1,15 @@
 class Object
   # Returns true if this object is included in the argument. Argument must be
-  # any object which respond to +#include?+. Usage:
+  # any object which responds to +#include?+. Usage:
   #
   #   characters = ["Konata", "Kagami", "Tsukasa"]
   #   "Konata".in?(characters) # => true
   #
+  # This will throw an ArgumentError if the argument doesn't respond
+  # to +#include?+.
   def in?(another_object)
     another_object.include?(self)
+  rescue NoMethodError
+    raise ArgumentError.new("The parameter passed to #in? must respond to #include?")
   end
 end