diff --git a/lib/query.js b/lib/query.js
index 1bfed85a27e..634616fe79a 100644
--- a/lib/query.js
+++ b/lib/query.js
@@ -4019,7 +4019,9 @@ Query.prototype._findAndModify = function(type, callback) {
  */
 
 function _completeOneLean(schema, doc, path, res, opts, callback) {
-  if (opts.lean && opts.lean.transform) {
+  if (opts.lean && typeof opts.lean.transform === 'function') {
+    opts.lean.transform(doc);
+
     for (let i = 0; i < schema.childSchemas.length; i++) {
       const childPath = path ? path + '.' + schema.childSchemas[i].model.path : schema.childSchemas[i].model.path;
       const _schema = schema.childSchemas[i].schema;
@@ -4053,7 +4055,11 @@ function _completeOneLean(schema, doc, path, res, opts, callback) {
  */
 
 function _completeManyLean(schema, docs, path, opts, callback) {
-  if (opts.lean && opts.lean.transform) {
+  if (opts.lean && typeof opts.lean.transform === 'function') {
+    for (const doc of docs) {
+      opts.lean.transform(doc);
+    }
+
     for (let i = 0; i < schema.childSchemas.length; i++) {
       const childPath = path ? path + '.' + schema.childSchemas[i].model.path : schema.childSchemas[i].model.path;
       const _schema = schema.childSchemas[i].schema;
diff --git a/test/query.test.js b/test/query.test.js
index 746774c5c42..1ebc5320aa4 100644
--- a/test/query.test.js
+++ b/test/query.test.js
@@ -4006,22 +4006,28 @@ describe('Query', function() {
     });
     const Test = db.model('gh10423', testSchema);
     await Test.create({ name: 'foo', foo: [{ sub: 'Test' }, { sub: 'Testerson' }], otherName: { nickName: 'Bar' } });
-    const result = await Test.find().lean({ transform: (doc) => {
-      delete doc._id;
-      return doc;
-    } });
-    assert(result[0]._id);
-    assert.equal(result[0].otherName._id, undefined);
-    assert.equal(result[0].foo[0]._id, undefined);
-    assert.equal(result[0].foo[1]._id, undefined);
-    const single = await Test.findOne().lean({ transform: (doc) => {
-      delete doc._id;
-      return doc;
-    } });
-    assert(single._id);
-    assert.equal(single.otherName._id, undefined);
-    assert.equal(single.foo[0]._id, undefined);
-    assert.equal(single.foo[0]._id, undefined);
+
+    const result = await Test.find().lean({
+      transform: (doc) => {
+        delete doc._id;
+        return doc;
+      }
+    });
+    assert.strictEqual(result[0]._id, undefined);
+    assert.strictEqual(result[0].otherName._id, undefined);
+    assert.strictEqual(result[0].foo[0]._id, undefined);
+    assert.strictEqual(result[0].foo[1]._id, undefined);
+
+    const single = await Test.findOne().lean({
+      transform: (doc) => {
+        delete doc._id;
+        return doc;
+      }
+    });
+    assert.strictEqual(single._id, undefined);
+    assert.strictEqual(single.otherName._id, undefined);
+    assert.strictEqual(single.foo[0]._id, undefined);
+    assert.strictEqual(single.foo[0]._id, undefined);
   });
 
   it('skips applying default projections over slice projections (gh-11940)', async function() {