diff --git a/src/utils.ts b/src/utils.ts
index 2295af40..9e26a35a 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -358,10 +358,12 @@ export function appendToDescription(existingDescription: string | undefined, ...
   return values.join('\n')
 }
 
-export function isSchemaLike(schema: LinkedJSONSchema) {
+export function isSchemaLike(schema: any): schema is LinkedJSONSchema {
   if (!isPlainObject(schema)) {
     return false
   }
+
+  // top-level schema
   const parent = schema[Parent]
   if (parent === null) {
     return true
diff --git a/test/testUtils.ts b/test/testUtils.ts
index 342de47a..ee252bd1 100644
--- a/test/testUtils.ts
+++ b/test/testUtils.ts
@@ -1,6 +1,5 @@
 import test from 'ava'
 import {link} from '../src/linker'
-import {LinkedJSONSchema} from '../src/types/JSONSchema'
 import {pathTransform, generateName, isSchemaLike} from '../src/utils'
 
 export function run() {
@@ -38,10 +37,10 @@ export function run() {
       required: ['firstName', 'lastName'],
     })
     t.is(isSchemaLike(schema), true)
-    t.is(isSchemaLike([] as any as LinkedJSONSchema), false)
-    t.is(isSchemaLike(schema.properties as LinkedJSONSchema), false)
-    t.is(isSchemaLike(schema.required as any as LinkedJSONSchema), false)
-    t.is(isSchemaLike(schema.title as any as LinkedJSONSchema), false)
+    t.is(isSchemaLike([]), false)
+    t.is(isSchemaLike(schema.properties), false)
+    t.is(isSchemaLike(schema.required), false)
+    t.is(isSchemaLike(schema.title), false)
     t.is(isSchemaLike(schema.properties!.firstName), true)
     t.is(isSchemaLike(schema.properties!.lastName), true)
   })