diff --git a/packages/language-service/src/typescript_symbols.ts b/packages/language-service/src/typescript_symbols.ts
index 2e4343206f..7928cfcf78 100644
--- a/packages/language-service/src/typescript_symbols.ts
+++ b/packages/language-service/src/typescript_symbols.ts
@@ -295,7 +295,8 @@ class TypeWrapper implements Symbol {
         if (nType) {
           // get the right tuple type by value, like 'var t: [number, string];'
           if (nType.isUnion()) {
-            return new TypeWrapper(nType.types[value], this.context);
+            // return undefined if array index out of bound.
+            return nType.types[value] && new TypeWrapper(nType.types[value], this.context);
           }
           return new TypeWrapper(nType, this.context);
         }
diff --git a/packages/language-service/test/diagnostics_spec.ts b/packages/language-service/test/diagnostics_spec.ts
index 0820891005..5a21eb43a2 100644
--- a/packages/language-service/test/diagnostics_spec.ts
+++ b/packages/language-service/test/diagnostics_spec.ts
@@ -159,6 +159,13 @@ describe('diagnostics', () => {
         .toBe(`Identifier 'badProperty' is not defined. 'Hero' does not contain such a member`);
   });
 
+  it('should not produce errors if tuple array index out of bound', () => {
+    mockHost.override(TEST_TEMPLATE, `
+        {{tupleArray[2].badProperty}}`);
+    const diags = ngLS.getDiagnostics(TEST_TEMPLATE);
+    expect(diags).toEqual([]);
+  });
+
   it('should not produce errors on function.bind()', () => {
     mockHost.override(TEST_TEMPLATE, `
       <test-comp (test)="myClick.bind(this)">