diff --git a/script/tool/lib/src/update_dependency_command.dart b/script/tool/lib/src/update_dependency_command.dart
index 30060bc228..d3914ca73b 100644
--- a/script/tool/lib/src/update_dependency_command.dart
+++ b/script/tool/lib/src/update_dependency_command.dart
@@ -170,9 +170,13 @@ ${response.httpResponse.body}
       if (!await _regeneratePigeonFiles(package)) {
         return PackageResult.fail(<String>['Failed to update pigeon files']);
       }
+    } else if (dependency == 'mockito') {
+      if (!await _regenerateMocks(package)) {
+        return PackageResult.fail(<String>['Failed to update mocks']);
+      }
     }
     // TODO(stuartmorgan): Add additional handling of known packages that
-    // do file generation (mockito, etc.).
+    // do file generation.
 
     return PackageResult.success();
   }
@@ -258,6 +262,43 @@ ${response.httpResponse.body}
     }
     return true;
   }
+
+  /// Re-runs Mockito mock generation for [package] if necessary.
+  Future<bool> _regenerateMocks(RepositoryPackage package) async {
+    final Pubspec pubspec = package.parsePubspec();
+    if (!pubspec.devDependencies.keys.contains('build_runner')) {
+      print(
+          '${indentation}No build_runner dependency; skipping mock regeneration.');
+      return true;
+    }
+
+    print('${indentation}Running pub get...');
+    final io.ProcessResult getResult = await processRunner
+        .run('dart', <String>['pub', 'get'], workingDir: package.directory);
+    if (getResult.exitCode != 0) {
+      printError('dart pub get failed (${getResult.exitCode}):\n'
+          '${getResult.stdout}\n${getResult.stderr}\n');
+      return false;
+    }
+
+    print('${indentation}Updating mocks...');
+    final io.ProcessResult buildRunnerResult = await processRunner.run(
+        'dart',
+        <String>[
+          'run',
+          'build_runner',
+          'build',
+          '--delete-conflicting-outputs'
+        ],
+        workingDir: package.directory);
+    if (buildRunnerResult.exitCode != 0) {
+      printError(
+          '"dart run build_runner build" failed (${buildRunnerResult.exitCode}):\n'
+          '${buildRunnerResult.stdout}\n${buildRunnerResult.stderr}\n');
+      return false;
+    }
+    return true;
+  }
 }
 
 class _PubDependencyInfo {
diff --git a/script/tool/test/update_dependency_command_test.dart b/script/tool/test/update_dependency_command_test.dart
index e0687b2bfd..c19c110e24 100644
--- a/script/tool/test/update_dependency_command_test.dart
+++ b/script/tool/test/update_dependency_command_test.dart
@@ -466,5 +466,122 @@ dev_dependencies:
         ]),
       );
     });
+
+    test('regenerates mocks when updating mockito if necessary', () async {
+      final RepositoryPackage package =
+          createFakePackage('a_package', packagesDir);
+      addDependency(package, 'mockito', version: '1.0.0');
+      addDevDependency(package, 'build_runner');
+
+      await runCapturingPrint(runner, <String>[
+        'update-dependency',
+        '--pub-package',
+        'mockito',
+        '--version',
+        '1.5.0',
+      ]);
+
+      expect(
+        processRunner.recordedCalls,
+        orderedEquals(<ProcessCall>[
+          ProcessCall(
+            'dart',
+            const <String>['pub', 'get'],
+            package.path,
+          ),
+          ProcessCall(
+            'dart',
+            const <String>[
+              'run',
+              'build_runner',
+              'build',
+              '--delete-conflicting-outputs'
+            ],
+            package.path,
+          ),
+        ]),
+      );
+    });
+
+    test('skips regenerating mocks when there is no build_runner dependency',
+        () async {
+      final RepositoryPackage package =
+          createFakePackage('a_package', packagesDir);
+      addDependency(package, 'mockito', version: '1.0.0');
+
+      await runCapturingPrint(runner, <String>[
+        'update-dependency',
+        '--pub-package',
+        'mockito',
+        '--version',
+        '1.5.0',
+      ]);
+
+      expect(processRunner.recordedCalls.isEmpty, true);
+    });
+
+    test('updating mockito fails if pub get fails', () async {
+      final RepositoryPackage package =
+          createFakePackage('a_package', packagesDir);
+      addDependency(package, 'mockito', version: '1.0.0');
+      addDevDependency(package, 'build_runner');
+
+      processRunner.mockProcessesForExecutable['dart'] = <FakeProcessInfo>[
+        FakeProcessInfo(MockProcess(exitCode: 1), <String>['pub', 'get'])
+      ];
+
+      Error? commandError;
+      final List<String> output = await runCapturingPrint(runner, <String>[
+        'update-dependency',
+        '--pub-package',
+        'mockito',
+        '--version',
+        '1.5.0',
+      ], errorHandler: (Error e) {
+        commandError = e;
+      });
+
+      expect(commandError, isA<ToolExit>());
+      expect(
+        output,
+        containsAllInOrder(<Matcher>[
+          contains('dart pub get failed'),
+          contains('Failed to update mocks'),
+        ]),
+      );
+    });
+
+    test('updating mockito fails if running build_runner fails', () async {
+      final RepositoryPackage package =
+          createFakePackage('a_package', packagesDir);
+      addDependency(package, 'mockito', version: '1.0.0');
+      addDevDependency(package, 'build_runner');
+
+      processRunner.mockProcessesForExecutable['dart'] = <FakeProcessInfo>[
+        FakeProcessInfo(MockProcess(), <String>['pub', 'get']),
+        FakeProcessInfo(
+            MockProcess(exitCode: 1), <String>['run', 'build_runner']),
+      ];
+
+      Error? commandError;
+      final List<String> output = await runCapturingPrint(runner, <String>[
+        'update-dependency',
+        '--pub-package',
+        'mockito',
+        '--version',
+        '1.5.0',
+      ], errorHandler: (Error e) {
+        commandError = e;
+      });
+
+      expect(commandError, isA<ToolExit>());
+      expect(
+        output,
+        containsAllInOrder(<Matcher>[
+          contains('"dart run build_runner build" failed'),
+          contains('Failed to update mocks'),
+        ]),
+      );
+    });
   });
 }