diff --git a/build/broccoli/write-smoke-test.js b/build/broccoli/write-smoke-test.js
index a027e99071..12037e2437 100644
--- a/build/broccoli/write-smoke-test.js
+++ b/build/broccoli/write-smoke-test.js
@@ -33,6 +33,8 @@ class TypesSmokeTestWriter extends Plugin {
           noUnusedLocals: true,
           noUnusedParameters: true,
           noImplicitReturns: true,
+          useDefineForClassFields: true,
+          exactOptionalPropertyTypes: true,
 
           newLine: 'LF',
           noEmit: true,
diff --git a/packages/@glimmer/syntax/lib/traversal/errors.ts b/packages/@glimmer/syntax/lib/traversal/errors.ts
index 6430f3ee21..48c9cf3e1a 100644
--- a/packages/@glimmer/syntax/lib/traversal/errors.ts
+++ b/packages/@glimmer/syntax/lib/traversal/errors.ts
@@ -7,7 +7,7 @@ export interface TraversalError extends Error {
   key: string;
   node: ASTv1.Node;
   parent: Option<ASTv1.Node>;
-  stack: string | undefined;
+  stack?: string | undefined;
 }
 
 export interface TraversalErrorConstructor {
diff --git a/packages/@glimmer/vm/tsconfig.json b/packages/@glimmer/vm/tsconfig.json
index a37bcb4f87..444404f867 100644
--- a/packages/@glimmer/vm/tsconfig.json
+++ b/packages/@glimmer/vm/tsconfig.json
@@ -19,6 +19,8 @@
     "noUnusedLocals": true,
     "noUnusedParameters": true,
     "noImplicitReturns": true,
+    "useDefineForClassFields": true,
+    "exactOptionalPropertyTypes": true,
 
     "newLine": "LF",
     "noEmit": true,
diff --git a/tsconfig.json b/tsconfig.json
index 1a2ed2f146..1b2b0645f5 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -22,7 +22,7 @@
     "noUnusedParameters": true,
     "noImplicitReturns": true,
     "useDefineForClassFields": true,
-    // "exactOptionalPropertyTypes": true,
+    "exactOptionalPropertyTypes": true,
     // "noImplicitOverride": true,
     // "noPropertyAccessFromIndexSignature": true,
     // "noUncheckedIndexedAccess": true,