diff --git a/README.md b/README.md
index dc6b9fd..dde41b0 100644
--- a/README.md
+++ b/README.md
@@ -8,6 +8,13 @@ Keeping these examples in a simple, isolated project lets me refer to known work
 
 New versions of Ansible are released regularly. The playbooks in this project are always tested against a specific version, which is specified in requirements.txt (e.g. `ansible==2.2.1.0`).
 
+## Server OS version
+
+These playbooks are tested against:
+
+* Vagrant boxes running a specific box version as specified in 'Vagrantfile', e.g. `config.vm.box_version = "v20170202.1.0"`
+* Digital Ocean machines running Ubuntu 14.04.5 x64
+
 ## Inventory
 
 See hosts/README.md for notes specific to inventory files.
diff --git a/Vagrantfile b/Vagrantfile
index 0d60b32..c081fd5 100644
--- a/Vagrantfile
+++ b/Vagrantfile
@@ -16,6 +16,7 @@ Vagrant.configure(2) do |config|
   end
 
   config.vm.box = "ubuntu/trusty64"
+  config.vm.box_version = "20170202.1.0"
 
   # Create a forwarded port mapping which allows access to a specific port
   # within the machine from a port on the host machine. In the example below,