diff --git a/lib/query.js b/lib/query.js
index 80e87994a57..45e6fb77f87 100644
--- a/lib/query.js
+++ b/lib/query.js
@@ -1359,7 +1359,7 @@ Query.prototype._find = function(callback) {
  *
  *     query.find({ name: 'Los Pollos Hermanos' }).find(callback)
  *
- * @param {Object} [criteria] mongodb selector
+ * @param {Object} [filter] mongodb selector
  * @param {Function} [callback]
  * @return {Query} this
  * @api public
@@ -1375,9 +1375,11 @@ Query.prototype.find = function(conditions, callback) {
 
   if (mquery.canMerge(conditions)) {
     this.merge(conditions);
-  }
 
-  prepareDiscriminatorCriteria(this);
+    prepareDiscriminatorCriteria(this);
+  } else if (conditions != null) {
+    this.error(new ObjectParameterError(conditions, 'filter', 'find'));
+  }
 
   // if we don't have a callback, then just return the query object
   if (!callback) {
@@ -1564,7 +1566,7 @@ Query.prototype._findOne = function(callback) {
  *       }
  *     });
  *
- * @param {Object|Query} [criteria] mongodb selector
+ * @param {Object} [filter] mongodb selector
  * @param {Object} [projection] optional fields to return
  * @param {Object} [options] see [`setOptions()`](http://mongoosejs.com/docs/api.html#query_Query-setOptions)
  * @param {Function} [callback] optional params are (error, document)
@@ -1604,18 +1606,17 @@ Query.prototype.findOne = function(conditions, projection, options, callback) {
 
   if (mquery.canMerge(conditions)) {
     this.merge(conditions);
-  } else if (conditions != null) {
-    throw new Error('Invalid argument to findOne(): ' +
-      util.inspect(conditions));
-  }
 
-  prepareDiscriminatorCriteria(this);
+    prepareDiscriminatorCriteria(this);
 
-  try {
-    this.cast(this.model);
-    this.error(null);
-  } catch (err) {
-    this.error(err);
+    try {
+      this.cast(this.model);
+      this.error(null);
+    } catch (err) {
+      this.error(err);
+    }
+  } else if (conditions != null) {
+    this.error(new ObjectParameterError(conditions, 'filter', 'findOne'));
   }
 
   if (!callback) {