diff --git a/lib/CachePlugin.js b/lib/CachePlugin.js
index ecbf4c4ce..73f215ced 100644
--- a/lib/CachePlugin.js
+++ b/lib/CachePlugin.js
@@ -63,6 +63,7 @@ CachePlugin.prototype.apply = function(compiler) {
 	}
 };
 
+/* istanbul ignore next */
 CachePlugin.prototype.applyMtime = function applyMtime(mtime) {
 	if(this.FS_ACCURENCY > 1 && mtime % 2 !== 0)
 		this.FS_ACCURENCY = 1;