diff --git a/activerecord/lib/active_record/reflection.rb b/activerecord/lib/active_record/reflection.rb
index 73d154e03e130..f428f160cf992 100644
--- a/activerecord/lib/active_record/reflection.rb
+++ b/activerecord/lib/active_record/reflection.rb
@@ -394,7 +394,7 @@ def inverse_name
         # returns either nil or the inverse association name that it finds.
         def automatic_inverse_of
           if can_find_inverse_of_automatically?(self)
-            inverse_name = active_record.name.downcase.to_sym
+            inverse_name = ActiveSupport::Inflector.underscore(active_record.name).to_sym
 
             begin
               reflection = klass.reflect_on_association(inverse_name)
@@ -413,7 +413,7 @@ def automatic_inverse_of
         end
 
         # Checks if the inverse reflection that is returned from the
-        # +set_automatic_inverse_of+ method is a valid reflection. We must
+        # +automatic_inverse_of+ method is a valid reflection. We must
         # make sure that the reflection's active_record name matches up
         # with the current reflection's klass name.
         #
diff --git a/activerecord/test/cases/associations/inverse_associations_test.rb b/activerecord/test/cases/associations/inverse_associations_test.rb
index ce78332124727..2477e60e51855 100644
--- a/activerecord/test/cases/associations/inverse_associations_test.rb
+++ b/activerecord/test/cases/associations/inverse_associations_test.rb
@@ -9,10 +9,24 @@
 require 'models/comment'
 require 'models/car'
 require 'models/bulb'
+require 'models/mixed_case_monkey'
 
 class AutomaticInverseFindingTests < ActiveRecord::TestCase
   fixtures :ratings, :comments, :cars
 
+  def test_has_one_and_belongs_to_should_find_inverse_automatically_on_multiple_word_name
+    monkey_reflection = MixedCaseMonkey.reflect_on_association(:man)
+    man_reflection = Man.reflect_on_association(:mixed_case_monkey)
+
+    assert_respond_to monkey_reflection, :has_inverse?
+    assert monkey_reflection.has_inverse?, "The monkey reflection should have an inverse"
+    assert_equal man_reflection, monkey_reflection.inverse_of, "The monkey reflection's inverse should be the man reflection"
+
+    assert_respond_to man_reflection, :has_inverse?
+    assert man_reflection.has_inverse?, "The man reflection should have an inverse"
+    assert_equal monkey_reflection, man_reflection.inverse_of, "The man reflection's inverse should be the monkey reflection"
+  end
+
   def test_has_one_and_belongs_to_should_find_inverse_automatically
     car_reflection = Car.reflect_on_association(:bulb)
     bulb_reflection = Bulb.reflect_on_association(:car)
diff --git a/activerecord/test/models/man.rb b/activerecord/test/models/man.rb
index 4bff92dc98bce..f4d127730c75c 100644
--- a/activerecord/test/models/man.rb
+++ b/activerecord/test/models/man.rb
@@ -6,4 +6,5 @@ class Man < ActiveRecord::Base
   # These are "broken" inverse_of associations for the purposes of testing
   has_one :dirty_face, :class_name => 'Face', :inverse_of => :dirty_man
   has_many :secret_interests, :class_name => 'Interest', :inverse_of => :secret_man
+  has_one :mixed_case_monkey
 end
diff --git a/activerecord/test/models/mixed_case_monkey.rb b/activerecord/test/models/mixed_case_monkey.rb
index 763baefd9181a..4d373717771cc 100644
--- a/activerecord/test/models/mixed_case_monkey.rb
+++ b/activerecord/test/models/mixed_case_monkey.rb
@@ -1,3 +1,5 @@
 class MixedCaseMonkey < ActiveRecord::Base
   self.primary_key = 'monkeyID'
+
+  belongs_to :man
 end