diff --git a/lib/execjs.rb b/lib/execjs.rb
index e6a3d09..8c55449 100644
--- a/lib/execjs.rb
+++ b/lib/execjs.rb
@@ -2,5 +2,7 @@
 require "execjs/runtimes"
 
 module ExecJS
-  self.runtime ||= Runtimes.autodetect
+  def self.runtime
+    @runtime ||= Runtimes.autodetect
+  end
 end
diff --git a/test/test_execjs.rb b/test/test_execjs.rb
index b0c4d07..f2a5e23 100644
--- a/test/test_execjs.rb
+++ b/test/test_execjs.rb
@@ -5,6 +5,7 @@
 
 begin
   require "execjs"
+  ExecJS.runtime
 rescue ExecJS::RuntimeUnavailable => e
   warn e
   exit 2