diff --git a/lib/stack_master/commands/apply.rb b/lib/stack_master/commands/apply.rb
index <HASH>..<HASH> 100644
--- a/lib/stack_master/commands/apply.rb
+++ b/lib/stack_master/commands/apply.rb
@@ -6,8 +6,8 @@ module StackMaster
 
       def initialize(config, region, stack_name)
         @config = config
-        @region = region
-        @stack_name = stack_name
+        @region = region.gsub('_', '-')
+        @stack_name = stack_name.gsub('_', '-')
       end
 
       def perform
diff --git a/spec/stack_master/commands/apply_spec.rb b/spec/stack_master/commands/apply_spec.rb
index <HASH>..<HASH> 100644
--- a/spec/stack_master/commands/apply_spec.rb
+++ b/spec/stack_master/commands/apply_spec.rb
@@ -1,7 +1,7 @@
 RSpec.describe StackMaster::Commands::Apply do
   let(:cf) { instance_double(Aws::CloudFormation::Client) }
   let(:region) { 'us-east-1' }
-  let(:stack_name) { 'myapp_vpc' }
+  let(:stack_name) { 'myapp-vpc' }
   let(:config) { double(find_stack: stack_definition) }
   let(:stack_definition) { StackMaster::Config::StackDefinition.new(
       region: 'us_east_1',
Ensure we replace underscores with hyphens