diff --git a/activesupport/lib/active_support/callbacks.rb b/activesupport/lib/active_support/callbacks.rb
index ee4b3fe6bb..e948314be7 100644
--- a/activesupport/lib/active_support/callbacks.rb
+++ b/activesupport/lib/active_support/callbacks.rb
@@ -314,7 +314,7 @@ module ActiveSupport
           @klass.send(:define_method, method_name, &filter)
           return method_name if filter.arity <= 0
 
-          method_name << (filter.arity == 1 ? "(self)" : " self, ::Proc.new ")
+          method_name << (filter.arity == 1 ? "(self)" : "(self, ::Proc.new)")
         else
           method_name = _method_name_for_object_filter(kind, filter)
           @klass.send(:define_method, "#{method_name}_object") { filter }
diff --git a/activesupport/test/callbacks_test.rb b/activesupport/test/callbacks_test.rb
index 0a79cb037c..b48145aab7 100644
--- a/activesupport/test/callbacks_test.rb
+++ b/activesupport/test/callbacks_test.rb
@@ -802,6 +802,46 @@ module CallbacksTest
     end
   end
 
+  class ConditionalTests < ActiveSupport::TestCase
+    def build_class(callback)
+      Class.new {
+        include ActiveSupport::Callbacks
+        define_callbacks :foo
+        set_callback :foo, :before, :foo, :if => callback
+        def foo; end
+        def run; run_callbacks :foo; end
+      }
+    end
+
+    def test_proc_negative_arity # passes an empty list if *args
+      z = []
+      object = build_class(->(*args) { z << args }).new
+      object.run
+      assert_equal [], z.flatten
+    end
+
+    def test_proc_arity0
+      z = []
+      object = build_class(->() { z << 0 }).new
+      object.run
+      assert_equal [0], z
+    end
+
+    def test_proc_arity1
+      z = []
+      object = build_class(->(x) { z << x }).new
+      object.run
+      assert_equal [object], z
+    end
+
+    def test_proc_arity2
+      assert_raises(ArgumentError) do
+        object = build_class(->(a,b) { }).new
+        object.run
+      end
+    end
+  end
+
   class CallbackTypeTest < ActiveSupport::TestCase
     def build_class(callback, n = 10)
       Class.new {