diff --git a/.circleci/config.yml b/.circleci/config.yml
index 91e3214cad..97788b2fed 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -678,7 +678,7 @@ jobs:
           background: true
       # add module umd tsc compile option so the test can work
       # properly in the legacy browsers
-      - run: yarn tsc -p packages --module UMD
+      - run: yarn tsc -p packages/tsconfig-legacy-saucelabs.json --module UMD
       - run: yarn tsc -p modules --module UMD
       - run: yarn bazel build //packages/zone.js:npm_package
       # Build test fixtures for a test that rely on Bazel-generated fixtures. Note that disabling
diff --git a/dev-infra/tsconfig.json b/dev-infra/tsconfig.json
index a107894e33..b5c32c096c 100644
--- a/dev-infra/tsconfig.json
+++ b/dev-infra/tsconfig.json
@@ -1,6 +1,8 @@
 {
   "compilerOptions": {
     "strict": true,
-    "downlevelIteration": true
+    "downlevelIteration": true,
+    "noImplicitAny": true,
+    "noImplicitOverride": true
   }
 }
diff --git a/packages/core/schematics/tsconfig.json b/packages/core/schematics/tsconfig.json
index 53930ff133..89cfe2bb70 100644
--- a/packages/core/schematics/tsconfig.json
+++ b/packages/core/schematics/tsconfig.json
@@ -1,6 +1,7 @@
 {
   "compilerOptions": {
     "noImplicitReturns": true,
+    "noImplicitOverride": true,
     "noFallthroughCasesInSwitch": true,
     "strict": true,
     "moduleResolution": "node",
diff --git a/packages/service-worker/cli/tsconfig.json b/packages/service-worker/cli/tsconfig.json
index 4b9edf0ef1..f7f78dabdb 100644
--- a/packages/service-worker/cli/tsconfig.json
+++ b/packages/service-worker/cli/tsconfig.json
@@ -9,6 +9,7 @@
     "strictPropertyInitialization": true,
     "outDir": "../../../dist/all/@angular/service-worker/cli-custom",
     "noImplicitAny": true,
+    "noImplicitOverride": true,
     "noFallthroughCasesInSwitch": true,
     "rootDir": ".",
     "paths": {
diff --git a/packages/tsconfig-build.json b/packages/tsconfig-build.json
index e9793106cc..7bfa7c1761 100644
--- a/packages/tsconfig-build.json
+++ b/packages/tsconfig-build.json
@@ -8,6 +8,7 @@
     "declaration": true,
     "stripInternal": true,
     "noImplicitAny": true,
+    "noImplicitOverride": true,
     "strictNullChecks": true,
     "strict": true,
     "strictPropertyInitialization": true,
diff --git a/packages/tsconfig-legacy-saucelabs.json b/packages/tsconfig-legacy-saucelabs.json
new file mode 100644
index 0000000000..55a8be3522
--- /dev/null
+++ b/packages/tsconfig-legacy-saucelabs.json
@@ -0,0 +1,11 @@
+{
+  "extends": "./tsconfig.json",
+  "compilerOptions": {
+    // The project uses Bazel for TypeScript compilation. Unlike with Bazel, we build all
+    // sources as part of a single TypeScript compilation. This results in `@internal`
+    // declarations not being omitted between the logical as defined per the Bazel targets.
+    // This can cause issues where the `override` keyword is needed for the legacy TS
+    // compilation, but not within Bazel where the overridden member has `@internal`.
+    "noImplicitOverride": false,
+  }
+}
diff --git a/packages/tsconfig.json b/packages/tsconfig.json
index ae0df22ad6..681addcbb2 100644
--- a/packages/tsconfig.json
+++ b/packages/tsconfig.json
@@ -14,6 +14,7 @@
     "strictPropertyInitialization": true,
     "outDir": "../dist/all/@angular",
     "noImplicitAny": true,
+    "noImplicitOverride": true,
     "noFallthroughCasesInSwitch": true,
     "paths": {
       "selenium-webdriver": ["./node_modules/@types/selenium-webdriver/index.d.ts"],
diff --git a/packages/zone.js/tsconfig.json b/packages/zone.js/tsconfig.json
index 6ee93c8e1e..abf52609e4 100644
--- a/packages/zone.js/tsconfig.json
+++ b/packages/zone.js/tsconfig.json
@@ -9,6 +9,7 @@
     "noEmitOnError": false,
     "stripInternal": false,
     "strict": true,
+    "noImplicitOverride": true,
     "lib": [
       "es5",
       "dom",