diff --git a/closure/goog/labs/mock/mock.js b/closure/goog/labs/mock/mock.js
index cd3062dfd2..f6c5508bd3 100644
--- a/closure/goog/labs/mock/mock.js
+++ b/closure/goog/labs/mock/mock.js
@@ -256,6 +256,10 @@ goog.labs.mock.formatValue_ = function(obj, opt_id) {
         output.push('NULL');
       } else if (typeof obj === 'string') {
         output.push('"' + indentMultiline(obj) + '"');
+      } else if (typeof obj === 'symbol') {
+        output.push(obj.toString());
+      } else if (typeof obj === 'bigint') {
+        output.push(obj.toString(10) + 'n');
       } else if (typeof obj === 'function') {
         const funcName = goog.labs.mock.getFunctionName_(obj);
         output.push('<function ' + funcName + '>');
diff --git a/closure/goog/labs/mock/mock_test.js b/closure/goog/labs/mock/mock_test.js
index 5228844726..0ab496f036 100644
--- a/closure/goog/labs/mock/mock_test.js
+++ b/closure/goog/labs/mock/mock_test.js
@@ -1322,6 +1322,28 @@ testSuite({
     assertEquals('{"x":<function y>}', mock.formatValue_(obj, false /* id */));
   },
 
+  /** @suppress {visibility} suppression added to enable type checking */
+  testFormatSymbols() {
+    if (typeof window['Symbol'] !== 'function') {
+      return;  // skip browsers without symbols
+    }
+    if (Symbol().toString() !== 'Symbol()') {
+      // skip testing in environments with a likely-polyfilled symbol,
+      // as their Symbol wouldn't have the right typeof value.
+      return;
+    }
+    assertEquals('Symbol()', mock.formatValue_(Symbol()));
+    assertEquals('Symbol(foobar)', mock.formatValue_(Symbol('foobar')));
+  },
+
+  /** @suppress {visibility} suppression added to enable type checking */
+  testFormatBigInts() {
+    if (typeof window['BigInt'] !== 'function') {
+      return;  // skip browsers without bigints
+    }
+    assertEquals('30n', mock.formatValue_(BigInt(30)));
+  },
+
   testGetUid() {
     const obj1 = {};
     const obj2 = {};