diff --git a/lib/util/resolve-schema-reference.js b/lib/util/resolve-schema-reference.js
index 06bf7757..5d9d85bc 100644
--- a/lib/util/resolve-schema-reference.js
+++ b/lib/util/resolve-schema-reference.js
@@ -6,7 +6,7 @@ function resolveSchemaReference (rawSchema, ref) {
   // Ref has format `#/definitions/id`
   const schemaId = resolvedReference?.$ref?.split('/', 3)[2]
 
-  if (schemaId === undefined) {
+  if (schemaId === undefined || resolvedReference.definitions === undefined) {
     return undefined
   }