2 files changed, 12 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/deprecation/behaviors.rb b/activesupport/lib/active_support/deprecation/behaviors.rb
index 66d6f3225a..3abd25aa85 100644
--- a/activesupport/lib/active_support/deprecation/behaviors.rb
+++ b/activesupport/lib/active_support/deprecation/behaviors.rb
@@ -94,6 +94,10 @@ module ActiveSupport
 
       private
         def arity_coerce(behavior)
+          unless behavior.respond_to?(:call)
+            raise ArgumentError, "#{behavior.inspect} is not a valid deprecation behavior."
+          end
+
           if behavior.arity == 4 || behavior.arity == -1
             behavior
           else
diff --git a/activesupport/test/deprecation_test.rb b/activesupport/test/deprecation_test.rb
index 60673c032b..105153584d 100644
--- a/activesupport/test/deprecation_test.rb
+++ b/activesupport/test/deprecation_test.rb
@@ -182,6 +182,14 @@ class DeprecationTest < ActiveSupport::TestCase
     end
   end
 
+  def test_default_invalid_behavior
+    e = assert_raises(ArgumentError) do
+      ActiveSupport::Deprecation.behavior = :invalid
+    end
+
+    assert_equal ":invalid is not a valid deprecation behavior.", e.message
+  end
+
   def test_deprecated_instance_variable_proxy
     assert_not_deprecated { @dtc.request.size }