diff --git a/lib/vagrant-hostmanager/hosts_file/updater.rb b/lib/vagrant-hostmanager/hosts_file/updater.rb
index 2ee2ad9..6048905 100644
--- a/lib/vagrant-hostmanager/hosts_file/updater.rb
+++ b/lib/vagrant-hostmanager/hosts_file/updater.rb
@@ -208,7 +208,7 @@ def self.windows?
           end
 
           def self.wsl?
-            defined?(ENV['WSLENV'])
+            ENV.include?('WSLENV')
           end
 
           require 'win32ole' if windows?