diff --git a/lib/document.js b/lib/document.js
index 78b6f58eff2..61a88edfe72 100644
--- a/lib/document.js
+++ b/lib/document.js
@@ -1388,6 +1388,7 @@ Document.prototype.$set = function $set(path, val, type, options) {
     if (schema.options &&
         Array.isArray(schema.options[typeKey]) &&
         schema.options[typeKey].length &&
+        schema.options[typeKey][0] &&
         schema.options[typeKey][0].ref &&
         _isManuallyPopulatedArray(val, schema.options[typeKey][0].ref)) {
       popOpts = { [populateModelSymbol]: val[0].constructor };