diff --git a/lib/caching-precompiler.js b/lib/caching-precompiler.js
index 0e7058ab3..c9497415c 100644
--- a/lib/caching-precompiler.js
+++ b/lib/caching-precompiler.js
@@ -50,8 +50,7 @@ CachingPrecompiler.prototype._factory = function (babelConfig, cacheDir) {
 			ast: false
 		});
 
-		options.plugins = options.plugins || [];
-		options.plugins.push(powerAssert, transformRuntime, rewriteRuntime);
+		options.plugins = (options.plugins || []).concat([powerAssert, transformRuntime, rewriteRuntime]);
 
 		return options;
 	}