diff --git a/lib/cast.js b/lib/cast.js
index 928fe9d1ba4..3dfd651acd2 100644
--- a/lib/cast.js
+++ b/lib/cast.js
@@ -27,6 +27,12 @@ module.exports = function cast(schema, obj, options, context) {
     throw new Error('Query filter must be an object, got an array ', util.inspect(obj));
   }
 
+  // bson 1.x has the unfortunate tendency to remove filters that have a top-level
+  // `_bsontype` property. Should remove this when we upgrade to bson 4.x. See gh-8222
+  if (obj.hasOwnProperty('_bsontype')) {
+    delete obj._bsontype;
+  }
+
   const paths = Object.keys(obj);
   let i = paths.length;
   let _keys;