diff --git a/lib/cli/options.js b/lib/cli/options.js
index a88dbfbf17..c7b73ff59d 100644
--- a/lib/cli/options.js
+++ b/lib/cli/options.js
@@ -230,6 +230,9 @@ const loadMochaOpts = (args = {}) => {
   // if there's an exception to catch here, I'm not sure what it is.
   // by attaching the `no-opts` arg, we avoid re-parsing of `mocha.opts`.
   if (mochaOpts) {
+    deprecate(
+      'Configuration via mocha.opts is DEPRECATED and will be removed from a future version of Mocha. Use RC files or package.json instead.'
+    );
     result = parse(parseMochaOpts(mochaOpts));
     debug(`${filepath} parsed succesfully`);
   }