diff --git a/lib/fog/compute/aws.rb b/lib/fog/compute/aws.rb
index 270de5b12..e5cd2e616 100644
--- a/lib/fog/compute/aws.rb
+++ b/lib/fog/compute/aws.rb
@@ -136,6 +136,11 @@ module Fog
           require 'fog/compute/parsers/aws/basic'
 
           @aws_access_key_id = options[:aws_access_key_id]
+
+        unless ['ap-northeast-1', 'ap-southeast-1', 'eu-west-1', 'us-east-1', 'us-west-1'].include?(options[:region])
+          raise ArgumentError, "Unknown region: #{options[:region].inspect}"
+        end
+
           @region = options[:region] || 'us-east-1'
 
           @data = self.class.data[@region][@aws_access_key_id]
diff --git a/lib/fog/compute/requests/aws/run_instances.rb b/lib/fog/compute/requests/aws/run_instances.rb
index 134ddddfe..0d5208303 100644
--- a/lib/fog/compute/requests/aws/run_instances.rb
+++ b/lib/fog/compute/requests/aws/run_instances.rb
@@ -133,7 +133,7 @@ module Fog
               # 'keyName'             => options['KeyName'],
               'launchTime'          => Time.now,
               'monitoring'          => { 'state' => options['Monitoring.Enabled'] || false },
-              'placement'           => { 'availabilityZone' => options['Placement.AvailabilityZone'] || Fog::AWS::Mock.availability_zone },
+              'placement'           => { 'availabilityZone' => options['Placement.AvailabilityZone'] || Fog::AWS::Mock.availability_zone(@region) },
               'privateDnsName'      => nil,
               'productCodes'        => [],
               'ramdiskId'           => options['RamdiskId'] || Fog::AWS::Mock.ramdisk_id,
diff --git a/lib/fog/providers/aws.rb b/lib/fog/providers/aws.rb
index 72e87be72..b7192d821 100644
--- a/lib/fog/providers/aws.rb
+++ b/lib/fog/providers/aws.rb
@@ -69,8 +69,8 @@ module Fog
 
     class Mock
 
-      def self.availability_zone
-        "us-east-1" << Fog::Mock.random_selection('abcd', 1)
+      def self.availability_zone(region)
+        "#{region}#{Fog::Mock.random_selection('abcd', 1)}"
       end
 
       def self.box_usage