diff --git a/lib/fog/aws.rb b/lib/fog/aws.rb
index 3219ef0d8..453eb09eb 100644
--- a/lib/fog/aws.rb
+++ b/lib/fog/aws.rb
@@ -46,6 +46,14 @@ module Fog
         sprintf("%0.10f", rand / 100).to_f
       end
 
+      def self.dns_name_for(ip_address)
+        "ec2-#{ip_address.gsub('.','-')}.compute-1.amazonaws.com"
+      end
+
+      def self.private_dns_name_for(ip_address)
+        "ip-#{ip_address.gsub('.','-')}.ec2.internal"
+      end
+
       def self.console_output
         'This is my console. There are many like it, but this one is mine. My console is my best friend. It is my life. I must master it as I master my life. My console, without me, is useless. Without my console, I am useless.'
       end
diff --git a/lib/fog/aws/requests/ec2/associate_address.rb b/lib/fog/aws/requests/ec2/associate_address.rb
index cbbf3d72a..011565dec 100644
--- a/lib/fog/aws/requests/ec2/associate_address.rb
+++ b/lib/fog/aws/requests/ec2/associate_address.rb
@@ -34,6 +34,9 @@ module Fog
           address = @data[:addresses][public_ip]
           if instance && address
             address['instanceId'] = instance_id
+            instance['originalIpAddress'] = instance['ipAddress']
+            instance['ipAddress'] = public_ip
+            instance['dnsName'] = Fog::AWS::Mock.dns_name_for(public_ip)
             response.status = 200
             response.body = {
               'requestId' => Fog::AWS::Mock.request_id,
diff --git a/lib/fog/aws/requests/ec2/describe_instances.rb b/lib/fog/aws/requests/ec2/describe_instances.rb
index dc1abfdd0..655429517 100644
--- a/lib/fog/aws/requests/ec2/describe_instances.rb
+++ b/lib/fog/aws/requests/ec2/describe_instances.rb
@@ -78,9 +78,9 @@ module Fog
               when 'pending'
                 if Time.now - instance['launchTime'] > Fog::Mock.delay
                   instance['ipAddress']         = Fog::AWS::Mock.ip_address
-                  instance['dnsName']           = "ec2-#{instance['ipAddress'].gsub('.','-')}.compute-1.amazonaws.com"
+                  instance['dnsName']           = Fog::AWS::Mock.dns_name_for(instance['ipAddress'])
                   instance['privateIpAddress']  = Fog::AWS::Mock.ip_address
-                  instance['privateDnsName']    = "ip-#{instance['privateIpAddress'].gsub('.','-')}.ec2.internal"
+                  instance['privateDnsName']    = Fog::AWS::Mock.private_dns_name_for(instance['privateIpAddress'])
                   instance['instanceState']     = { 'code' => 16, 'name' => 'running' }
                 end
               when 'rebooting'
diff --git a/lib/fog/aws/requests/ec2/disassociate_address.rb b/lib/fog/aws/requests/ec2/disassociate_address.rb
index d1c6e6265..41b42e6d7 100644
--- a/lib/fog/aws/requests/ec2/disassociate_address.rb
+++ b/lib/fog/aws/requests/ec2/disassociate_address.rb
@@ -29,6 +29,10 @@ module Fog
           response = Excon::Response.new
           response.status = 200
           if address = @data[:addresses][public_ip]
+            instance_id = address['instanceId']
+            instance = @data[:instances][instance_id]
+            instance['ipAddress']         = instance['originalIpAddress']
+            instance['dnsName']           = Fog::AWS::Mock.dns_name_for(instance['ipAddress'])
             address['instanceId'] = nil
             response.status = 200
             response.body = {
diff --git a/tests/aws/requests/ec2/address_tests.rb b/tests/aws/requests/ec2/address_tests.rb
index e524817b0..bb0f10fef 100644
--- a/tests/aws/requests/ec2/address_tests.rb
+++ b/tests/aws/requests/ec2/address_tests.rb
@@ -2,6 +2,7 @@ Shindo.tests('AWS::EC2 | address requests', ['aws']) do
 
   @server = AWS[:ec2].servers.create(:image_id => GENTOO_AMI)
   @server.wait_for { ready? }
+  @ip_address = @server.ip_address
 
   tests('success') do
 
@@ -32,11 +33,13 @@ Shindo.tests('AWS::EC2 | address requests', ['aws']) do
     test("#associate_address('#{@server.identity}', '#{@public_ip}')") do
       @data = AWS[:ec2].associate_address(@server.identity, @public_ip).body
       has_format(@data, AWS::EC2::Formats::BASIC)
+      @server.reload.ip_address == @public_ip
     end
 
     test("#disassociate_address('#{@public_ip}')") do
       @data = AWS[:ec2].disassociate_address(@public_ip).body
       has_format(@data, AWS::EC2::Formats::BASIC)
+      @server.reload.ip_address == @ip_address
     end
 
     test("#release_address('#{@public_ip}')") do