diff --git a/build/gulpfile.editor.js b/build/gulpfile.editor.js
index f6106241ced..6cb65c5a166 100644
--- a/build/gulpfile.editor.js
+++ b/build/gulpfile.editor.js
@@ -127,6 +127,7 @@ const createESMSourcesAndResourcesTask = task.define('extract-editor-esm', () =>
 
 const compileEditorESMTask = task.define('compile-editor-esm', () => {
 	const KEEP_PREV_ANALYSIS = false;
+	const FAIL_ON_PURPOSE = false;
 	console.log(`Launching the TS compiler at ${path.join(__dirname, '../out-editor-esm')}...`);
 	let result;
 	if (process.platform === 'win32') {
@@ -142,7 +143,7 @@ const compileEditorESMTask = task.define('compile-editor-esm', () => {
 	console.log(result.stdout.toString());
 	console.log(result.stderr.toString());
 
-	if (result.status !== 0) {
+	if (FAIL_ON_PURPOSE || result.status !== 0) {
 		console.log(`The TS Compilation failed, preparing analysis folder...`);
 		const destPath = path.join(__dirname, '../../vscode-monaco-editor-esm-analysis');
 		const keepPrevAnalysis = (KEEP_PREV_ANALYSIS && fs.existsSync(destPath));
diff --git a/build/lib/treeshaking.js b/build/lib/treeshaking.js
index cd366b9c524..5b1cf0591ec 100644
--- a/build/lib/treeshaking.js
+++ b/build/lib/treeshaking.js
@@ -420,7 +420,7 @@ function markNodes(languageService, options) {
                         // (they can be the declaration of a module import)
                         continue;
                     }
-                    if (options.shakeLevel === 2 /* ClassMembers */ && (ts.isClassDeclaration(declaration) || ts.isInterfaceDeclaration(declaration))) {
+                    if (options.shakeLevel === 2 /* ClassMembers */ && (ts.isClassDeclaration(declaration) || ts.isInterfaceDeclaration(declaration)) && !isLocalCodeExtendingOrInheritingFromDefaultLibSymbol(program, checker, declaration)) {
                         enqueue_black(declaration.name);
                         for (let j = 0; j < declaration.members.length; j++) {
                             const member = declaration.members[j];
@@ -614,6 +614,34 @@ function generateResult(languageService, shakeLevel) {
 }
 //#endregion
 //#region Utils
+function isLocalCodeExtendingOrInheritingFromDefaultLibSymbol(program, checker, declaration) {
+    if (!program.isSourceFileDefaultLibrary(declaration.getSourceFile()) && declaration.heritageClauses) {
+        for (const heritageClause of declaration.heritageClauses) {
+            for (const type of heritageClause.types) {
+                const symbol = findSymbolFromHeritageType(checker, type);
+                if (symbol) {
+                    const decl = symbol.valueDeclaration || (symbol.declarations && symbol.declarations[0]);
+                    if (decl && program.isSourceFileDefaultLibrary(decl.getSourceFile())) {
+                        return true;
+                    }
+                }
+            }
+        }
+    }
+    return false;
+}
+function findSymbolFromHeritageType(checker, type) {
+    if (ts.isExpressionWithTypeArguments(type)) {
+        return findSymbolFromHeritageType(checker, type.expression);
+    }
+    if (ts.isIdentifier(type)) {
+        return getRealNodeSymbol(checker, type)[0];
+    }
+    if (ts.isPropertyAccessExpression(type)) {
+        return findSymbolFromHeritageType(checker, type.name);
+    }
+    return null;
+}
 /**
  * Returns the node's symbol and the `import` node (if the symbol resolved from a different module)
  */
diff --git a/build/lib/treeshaking.ts b/build/lib/treeshaking.ts
index b65475299f5..405336bfcbb 100644
--- a/build/lib/treeshaking.ts
+++ b/build/lib/treeshaking.ts
@@ -536,7 +536,7 @@ function markNodes(languageService: ts.LanguageService, options: ITreeShakingOpt
 						continue;
 					}
 
-					if (options.shakeLevel === ShakeLevel.ClassMembers && (ts.isClassDeclaration(declaration) || ts.isInterfaceDeclaration(declaration))) {
+					if (options.shakeLevel === ShakeLevel.ClassMembers && (ts.isClassDeclaration(declaration) || ts.isInterfaceDeclaration(declaration)) && !isLocalCodeExtendingOrInheritingFromDefaultLibSymbol(program, checker, declaration)) {
 						enqueue_black(declaration.name!);
 
 						for (let j = 0; j < declaration.members.length; j++) {
@@ -752,6 +752,36 @@ function generateResult(languageService: ts.LanguageService, shakeLevel: ShakeLe
 
 //#region Utils
 
+function isLocalCodeExtendingOrInheritingFromDefaultLibSymbol(program: ts.Program, checker: ts.TypeChecker, declaration: ts.ClassDeclaration | ts.InterfaceDeclaration): boolean {
+	if (!program.isSourceFileDefaultLibrary(declaration.getSourceFile()) && declaration.heritageClauses) {
+		for (const heritageClause of declaration.heritageClauses) {
+			for (const type of heritageClause.types) {
+				const symbol = findSymbolFromHeritageType(checker, type);
+				if (symbol) {
+					const decl = symbol.valueDeclaration || (symbol.declarations && symbol.declarations[0]);
+					if (decl && program.isSourceFileDefaultLibrary(decl.getSourceFile())) {
+						return true;
+					}
+				}
+			}
+		}
+	}
+	return false;
+}
+
+function findSymbolFromHeritageType(checker: ts.TypeChecker, type: ts.ExpressionWithTypeArguments | ts.Expression | ts.PrivateIdentifier): ts.Symbol | null {
+	if (ts.isExpressionWithTypeArguments(type)) {
+		return findSymbolFromHeritageType(checker, type.expression);
+	}
+	if (ts.isIdentifier(type)) {
+		return getRealNodeSymbol(checker, type)[0];
+	}
+	if (ts.isPropertyAccessExpression(type)) {
+		return findSymbolFromHeritageType(checker, type.name);
+	}
+	return null;
+}
+
 /**
  * Returns the node's symbol and the `import` node (if the symbol resolved from a different module)
  */