diff --git a/spec/default_spec.rb b/spec/default_spec.rb
index 133b44c..887b3a9 100644
--- a/spec/default_spec.rb
+++ b/spec/default_spec.rb
@@ -6,8 +6,8 @@ describe 'postfix::default' do
   end
 
   context 'on Centos 6' do
-    let(:chef_run) do
-      ChefSpec::ServerRunner.new(platform: 'centos', version: 6.7).converge(described_recipe)
+    cached(:chef_run) do
+      ChefSpec::SoloRunner.new(platform: 'centos', version: 6.9).converge(described_recipe)
     end
 
     it '[COOK-4423] renders file main.cf with /etc/pki/tls/cert.pem' do
@@ -20,7 +20,7 @@ describe 'postfix::default' do
   end
 
   context 'on SmartOS' do
-    let(:chef_run) do
+    cached(:chef_run) do
       ChefSpec::ServerRunner.new(platform: 'smartos', version: '5.11').converge(described_recipe)
     end
 
@@ -34,7 +34,7 @@ describe 'postfix::default' do
   end
 
   context 'on Ubuntu 16.04' do
-    let(:chef_run) do
+    cached(:chef_run) do
       ChefSpec::ServerRunner.new(platform: 'ubuntu', version: 16.04).converge(described_recipe)
     end
 
diff --git a/spec/sasl_auth_spec.rb b/spec/sasl_auth_spec.rb
index bcb0991..6463085 100644
--- a/spec/sasl_auth_spec.rb
+++ b/spec/sasl_auth_spec.rb
@@ -3,7 +3,7 @@ require 'spec_helper'
 describe 'postfix::sasl_auth' do
   let(:password_file) { '/etc/postfix/sasl_passwd' }
 
-  let(:chef_run) do
+  cached(:chef_run) do
     ChefSpec::ServerRunner.new(platform: 'ubuntu', version: 16.04) do |node|
       node.default['postfix']['sasl_password_file'] = password_file
     end.converge(described_recipe)