diff --git a/activemodel/lib/active_model/observing.rb b/activemodel/lib/active_model/observing.rb
index 32f2aa46bd..b905d2b6d2 100644
--- a/activemodel/lib/active_model/observing.rb
+++ b/activemodel/lib/active_model/observing.rb
@@ -4,6 +4,7 @@
 require 'active_support/core_ext/module/remove_method'
 require 'active_support/core_ext/string/inflections'
 require 'active_support/core_ext/enumerable'
+require 'active_support/deprecation'
 require 'active_support/descendants_tracker'
 
 module ActiveModel
@@ -74,10 +75,16 @@ def notify_observers(*arg)
       end
 
       # Total number of observers.
-      def count_observers
+      def observers_count
         observer_instances.size
       end
 
+      def count_observers
+        msg = "count_observers is deprecated in favor of observers_count"
+        ActiveSupport::Deprecation.warn(msg)
+        observers_count
+      end
+
       protected
         def instantiate_observer(observer) #:nodoc:
           # string/symbol
diff --git a/activemodel/test/cases/observing_test.rb b/activemodel/test/cases/observing_test.rb
index f6ec24ae57..df070d2d8e 100644
--- a/activemodel/test/cases/observing_test.rb
+++ b/activemodel/test/cases/observing_test.rb
@@ -73,7 +73,7 @@ def setup
   test "passes observers to subclasses" do
     FooObserver.instance
     bar = Class.new(Foo)
-    assert_equal Foo.count_observers, bar.count_observers
+    assert_equal Foo.observers_count, bar.observers_count
   end
 end