diff --git a/index.js b/index.js
index 6a0559d..388a963 100644
--- a/index.js
+++ b/index.js
@@ -171,7 +171,7 @@ module.exports = function (args, opts) {
                     setArg(key, args[i+1], arg);
                     i++;
                 }
-                else if (args[i+1] && /true|false/.test(args[i+1])) {
+                else if (args[i+1] && /^(true|false)$/.test(args[i+1])) {
                     setArg(key, args[i+1] === 'true', arg);
                     i++;
                 }