diff --git a/activemodel/lib/active_model/observing.rb b/activemodel/lib/active_model/observing.rb
index 4682ae07ef4149f039fa09666a4113dd9bbae1a7..b94ad4bb9bbb0189e429ec382526815838dabbb7 100644
--- a/activemodel/lib/active_model/observing.rb
+++ b/activemodel/lib/active_model/observing.rb
@@ -71,9 +71,7 @@ def add_observer(observer)
 
       # Notify list of observers of a change.
       def notify_observers(*arg)
-        for observer in observer_instances
-          observer.update(*arg)
-        end
+        observer_instances.each { |observer| observer.update(*arg) }
       end
 
       # Total number of observers.