diff --git a/packages/mocha-runner/src/MochaOptionsLoader.ts b/packages/mocha-runner/src/MochaOptionsLoader.ts
index 2e683c5dcb..135833081b 100644
--- a/packages/mocha-runner/src/MochaOptionsLoader.ts
+++ b/packages/mocha-runner/src/MochaOptionsLoader.ts
@@ -34,6 +34,7 @@ export default class MochaOptionsLoader {
       this.log.debug('Mocha >= 6 detected. Using mocha\'s `%s` to load mocha options', LibWrapper.loadOptions.name);
       return this.loadMocha6Options(overrides);
     } else {
+      this.log.warn('DEPRECATED: Mocha < 6 detected. Please upgrade to at least Mocha version 6.');
       this.log.debug('Mocha < 6 detected. Using custom logic to parse mocha options');
       return this.loadLegacyMochaOptsFile(overrides.opts);
     }
diff --git a/packages/mocha-runner/test/unit/MochaOptionsLoader.spec.ts b/packages/mocha-runner/test/unit/MochaOptionsLoader.spec.ts
index a88c853b42..80c6ede4ab 100644
--- a/packages/mocha-runner/test/unit/MochaOptionsLoader.spec.ts
+++ b/packages/mocha-runner/test/unit/MochaOptionsLoader.spec.ts
@@ -113,6 +113,12 @@ describe(MochaOptionsLoader.name, () => {
       expect(testInjector.logger.debug).calledWith('Mocha < 6 detected. Using custom logic to parse mocha options');
     });
 
+    it('should log deprecated mocha version warning', async () => {
+      existsFileStub.returns(false);
+      sut.load(config);
+      expect(testInjector.logger.warn).calledWith('DEPRECATED: Mocha < 6 detected. Please upgrade to at least Mocha version 6.');
+    });
+
     it('should load a mocha.opts file if specified', () => {
       readFileStub.returns('');
       config.mochaOptions = {