diff --git a/lib/cli/options.js b/lib/cli/options.js
index fc0c951a8c..7886b510a8 100644
--- a/lib/cli/options.js
+++ b/lib/cli/options.js
@@ -110,15 +110,19 @@ const parse = (args = [], defaultValues = {}, ...configObjects) => {
   // 4. we can then reapply the values after yargs-parser is done.
   const nodeArgs = (Array.isArray(args) ? args : args.split(' ')).reduce(
     (acc, arg) => {
-      const pair = arg.split('=');
-      let flag = pair[0];
-      if (isNodeFlag(flag, false)) {
-        flag = flag.replace(/^--?/, '');
-        return arg.includes('=')
-          ? acc.concat([[flag, pair[1]]])
-          : acc.concat([[flag, true]]);
+      try {
+        const pair = arg.split('=');
+        let flag = pair[0];
+        if (isNodeFlag(flag, false)) {
+          flag = flag.replace(/^--?/, '');
+          return arg.includes('=')
+            ? acc.concat([[flag, pair[1]]])
+            : acc.concat([[flag, true]]);
+        }
+        return acc;
+      } catch (err) {
+        throw new Error(`Invalid option ${arg} passed to mocha cli`);
       }
-      return acc;
     },
     []
   );
@@ -192,8 +196,7 @@ const loadPkgRc = (args = {}) => {
           filepath
         );
       } else {
-        debug('failed to read default package.json at %s; ignoring',
-              filepath);
+        debug('failed to read default package.json at %s; ignoring', filepath);
         return result;
       }
     }
diff --git a/test/node-unit/cli/options.spec.js b/test/node-unit/cli/options.spec.js
index 7c846a37ed..22ed6830bb 100644
--- a/test/node-unit/cli/options.spec.js
+++ b/test/node-unit/cli/options.spec.js
@@ -204,9 +204,7 @@ describe('options', function () {
             const filepath = '/some/package.json';
             readFileSync = sinon.stub();
             // package.json
-            readFileSync
-              .onFirstCall()
-              .returns('{definitely-invalid');
+            readFileSync.onFirstCall().returns('{definitely-invalid');
             findConfig = sinon.stub().returns('/some/.mocharc.json');
             loadConfig = sinon.stub().returns({});
             findupSync = sinon.stub().returns(filepath);
@@ -224,7 +222,7 @@ describe('options', function () {
                 loadOptions();
               },
               'to throw',
-                /SyntaxError/,
+              /SyntaxError/
             );
           });
         });
@@ -676,5 +674,48 @@ describe('options', function () {
         ]);
       });
     });
+
+    describe('"numerical arguments"', function () {
+      const numericalArg = 123;
+
+      beforeEach(function () {
+        readFileSync = sinon.stub();
+        findConfig = sinon.stub();
+        loadConfig = sinon.stub();
+        findupSync = sinon.stub();
+        loadOptions = proxyLoadOptions({
+          readFileSync,
+          findConfig,
+          loadConfig,
+          findupSync
+        });
+      });
+
+      it('throws error when numerical option is passed to cli', function () {
+        expect(() => loadOptions(`${numericalArg}`), 'to throw', {
+          message: `Invalid option ${numericalArg} passed to mocha cli`
+        });
+      });
+
+      it('throws error when numerical argument is passed to mocha flag that does not accept numerical value', function () {
+        expect(() => loadOptions(`--delay ${numericalArg}`), 'to throw', {
+          message: `Invalid option ${numericalArg} passed to mocha cli`
+        });
+      });
+
+      it('does not throw error if numerical value is passed to a compatible mocha flag', function () {
+        expect(() => loadOptions(`--retries ${numericalArg}`), 'not to throw');
+      });
+
+      it('does not throw error if numerical value is passed to a node options', function () {
+        expect(
+          () =>
+            loadOptions(
+              `--secure-heap-min=${numericalArg} --conditions=${numericalArg}`
+            ),
+          'not to throw'
+        );
+      });
+    });
   });
 });