9 files changed, 25 insertions, 6 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 9239facf6..48b174c0f 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1375,9 +1375,9 @@ dependencies = [
 
 [[package]]
 name = "deno_config"
-version = "0.34.2"
+version = "0.34.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "764368ba1424ea74f9a28d8e2e7633f57d008e73f76b12bc272f6d5903ca1e08"
+checksum = "187d7dd888a49bfda396632371139e940c5cf47b15bfcaeeb2ba50f82f6940ec"
 dependencies = [
  "anyhow",
  "deno_package_json",
diff --git a/cli/Cargo.toml b/cli/Cargo.toml
index 40e3844c2..057b601ff 100644
--- a/cli/Cargo.toml
+++ b/cli/Cargo.toml
@@ -65,7 +65,7 @@ winres.workspace = true
 [dependencies]
 deno_ast = { workspace = true, features = ["bundler", "cjs", "codegen", "proposal", "react", "sourcemap", "transforms", "typescript", "view", "visit"] }
 deno_cache_dir = { workspace = true }
-deno_config = { version = "=0.34.2", features = ["workspace", "sync"] }
+deno_config = { version = "=0.34.3", features = ["workspace", "sync"] }
 deno_core = { workspace = true, features = ["include_js_files_for_snapshotting"] }
 deno_doc = { version = "0.148.0", features = ["html", "syntect"] }
 deno_graph = { version = "=0.82.1" }
diff --git a/cli/lsp/config.rs b/cli/lsp/config.rs
index f69cae435..94fdff167 100644
--- a/cli/lsp/config.rs
+++ b/cli/lsp/config.rs
@@ -1129,6 +1129,7 @@ impl Default for LspTsConfig {
         "module": "esnext",
         "moduleDetection": "force",
         "noEmit": true,
+        "noImplicitOverride": true,
         "resolveJsonModule": true,
         "strict": true,
         "target": "esnext",
diff --git a/cli/schemas/config-file.v1.json b/cli/schemas/config-file.v1.json
index 8d0af55bf..96b7c4bed 100644
--- a/cli/schemas/config-file.v1.json
+++ b/cli/schemas/config-file.v1.json
@@ -127,7 +127,7 @@
         "noImplicitOverride": {
           "description": "Ensure overriding members in derived classes are marked with an override modifier.",
           "type": "boolean",
-          "default": false,
+          "default": true,
           "markdownDescription": "Ensure overriding members in derived classes are marked with an override modifier.\n\nSee more: https://www.typescriptlang.org/tsconfig#noImplicitOverride"
         },
         "noImplicitReturns": {
diff --git a/cli/tsc/99_main_compiler.js b/cli/tsc/99_main_compiler.js
index c5769168f..719f2b982 100644
--- a/cli/tsc/99_main_compiler.js
+++ b/cli/tsc/99_main_compiler.js
@@ -1154,6 +1154,7 @@ delete Object.prototype.__proto__;
         "moduleResolution": "NodeNext",
         "moduleDetection": "force",
         "noEmit": true,
+        "noImplicitOverride": true,
         "resolveJsonModule": true,
         "strict": true,
         "target": "esnext",
diff --git a/tests/specs/check/no_implicit_override/__test__.jsonc b/tests/specs/check/no_implicit_override/__test__.jsonc
new file mode 100644
index 000000000..a991c6eed
--- /dev/null
+++ b/tests/specs/check/no_implicit_override/__test__.jsonc
@@ -0,0 +1,5 @@
+{
+  "args": "check main.ts",
+  "output": "main.out",
+  "exitCode": 1
+}
diff --git a/tests/specs/check/no_implicit_override/main.out b/tests/specs/check/no_implicit_override/main.out
new file mode 100644
index 000000000..6fd657341
--- /dev/null
+++ b/tests/specs/check/no_implicit_override/main.out
@@ -0,0 +1,5 @@
+Check file:///[WILDCARD]/main.ts
+error: TS4114 [ERROR]: This member must have an 'override' modifier because it overrides a member in the base class 'Greet'.
+  greet() {}
+  ~~~~~
+    at file:///[WILDCARD]/no_implicit_override/main.ts:6:3
diff --git a/tests/specs/check/no_implicit_override/main.ts b/tests/specs/check/no_implicit_override/main.ts
new file mode 100644
index 000000000..b51dfb9d9
--- /dev/null
+++ b/tests/specs/check/no_implicit_override/main.ts
@@ -0,0 +1,7 @@
+class Greet {
+  greet() {}
+}
+
+class Welcome extends Greet {
+  greet() {}
+}
diff --git a/tests/unit/url_search_params_test.ts b/tests/unit/url_search_params_test.ts
index c547ef938..d682c291a 100644
--- a/tests/unit/url_search_params_test.ts
+++ b/tests/unit/url_search_params_test.ts
@@ -330,7 +330,7 @@ Deno.test(
   function urlSearchParamsOverridingAppendNotChangeConstructorAndSet() {
     let overriddenAppendCalled = 0;
     class CustomSearchParams extends URLSearchParams {
-      append(name: string, value: string) {
+      override append(name: string, value: string) {
         ++overriddenAppendCalled;
         super.append(name, value);
       }
@@ -345,7 +345,7 @@ Deno.test(
 
 Deno.test(function urlSearchParamsOverridingEntriesNotChangeForEach() {
   class CustomSearchParams extends URLSearchParams {
-    *entries(): IterableIterator<[string, string]> {
+    override *entries(): IterableIterator<[string, string]> {
       yield* [];
     }
   }