diff --git a/lib/fog/aws/models/auto_scaling/group.rb b/lib/fog/aws/models/auto_scaling/group.rb
index 97843dcc7..57fc6a604 100644
--- a/lib/fog/aws/models/auto_scaling/group.rb
+++ b/lib/fog/aws/models/auto_scaling/group.rb
@@ -132,7 +132,7 @@ module Fog
 
         def update
           requires :id
-          service.update_auto_scaling_group(id, options)
+          service.update_auto_scaling_group(id, options.reject{|k,v| k == "Instances" })
           reload
         end
 
diff --git a/lib/fog/aws/requests/auto_scaling/update_auto_scaling_group.rb b/lib/fog/aws/requests/auto_scaling/update_auto_scaling_group.rb
index d3beb75ab..716f43235 100644
--- a/lib/fog/aws/requests/auto_scaling/update_auto_scaling_group.rb
+++ b/lib/fog/aws/requests/auto_scaling/update_auto_scaling_group.rb
@@ -71,6 +71,9 @@ module Fog
       class Mock
 
         def update_auto_scaling_group(auto_scaling_group_name, options = {})
+          if options.has_key?("Instances")
+            raise Fog::AWS::AutoScaling::ValidationError.new('Instances should not be included in request')
+          end
           unless self.data[:auto_scaling_groups].has_key?(auto_scaling_group_name)
             raise Fog::AWS::AutoScaling::ValidationError.new('AutoScalingGroup name not found - null')
           end
diff --git a/tests/aws/models/auto_scaling/groups_test.rb b/tests/aws/models/auto_scaling/groups_test.rb
new file mode 100644
index 000000000..43874727f
--- /dev/null
+++ b/tests/aws/models/auto_scaling/groups_test.rb
@@ -0,0 +1,22 @@
+Shindo.tests('AWS::AutoScaling | group', ['aws', 'auto_scaling_m']) do
+
+  params = {
+    :id => uniq_id,
+    :auto_scaling_group_name => "name",
+    :availability_zones => [],
+    :launch_configuration_name => "lc"
+  }
+
+  lc_params = {
+    :id => params[:launch_configuration_name],
+    :image_id => "image-id",
+    :instance_type => "instance-type",
+  }
+
+  Fog::AWS[:auto_scaling].configurations.new(lc_params).save
+  
+  model_tests(Fog::AWS[:auto_scaling].groups, params, true) do
+    @instance.update
+  end
+
+end