diff --git a/lib/active_model/serializable/utils.rb b/lib/active_model/serializable/utils.rb
index 7471bd0f..efabb6c4 100644
--- a/lib/active_model/serializable/utils.rb
+++ b/lib/active_model/serializable/utils.rb
@@ -4,8 +4,12 @@ module ActiveModel
       extend self
 
       def _const_get(const)
-        method = RUBY_VERSION >= '2.0' ? :const_get : :qualified_const_get
-        Object.send method, const
+        begin
+          method = RUBY_VERSION >= '2.0' ? :const_get : :qualified_const_get
+          Object.send method, const
+        rescue NameError
+          const.safe_constantize
+        end
       end
     end
   end
diff --git a/lib/active_model/serializer.rb b/lib/active_model/serializer.rb
index 689e132a..dd82e976 100644
--- a/lib/active_model/serializer.rb
+++ b/lib/active_model/serializer.rb
@@ -63,11 +63,7 @@ end
             ArraySerializer
           end
         else
-          begin
-            _const_get build_serializer_class(resource, options)
-          rescue NameError
-            nil
-          end
+          _const_get build_serializer_class(resource, options)
         end
       end