diff --git a/test/data-model.test.ts b/test/data-model.test.ts
index b7fb794..2d1d9e6 100644
--- a/test/data-model.test.ts
+++ b/test/data-model.test.ts
@@ -94,10 +94,10 @@
     }
   });
 
-  const assertions = MUSTS.assertions as [string];
+  const assertions = MUSTS['assertions'] as [string];
   assertions.forEach((schemaPath: string) => {
     const schema = requireJSON(`web-annotation-tests/${schemaPath}`);
-    it(schema.title as string, () => {
+    it(schema['title'] as string, () => {
       const valid = ajv.validate(schema, data);
       assert.isOk(valid, ajv.errorsText());
     });
diff --git a/tsconfig.base.json b/tsconfig.base.json
index 0c8a2ae..3070cfb 100644
--- a/tsconfig.base.json
+++ b/tsconfig.base.json
@@ -14,6 +14,7 @@
       "es2020"
     ],
     "moduleResolution": "node",
+    "noPropertyAccessFromIndexSignature": true,
     "skipLibCheck": true,
     "strict": true,
     "target": "es2017"