diff --git a/lib/document.js b/lib/document.js
index dce56008b3d..f59a1bb617e 100644
--- a/lib/document.js
+++ b/lib/document.js
@@ -2606,7 +2606,8 @@ Document.prototype.$markValid = function(path) {
 };
 
 /**
- * Saves this document.
+ * Saves this document by inserting a new document into the database if [document.isNew](/docs/api.html#document_Document-isNew) is `true`,
+ * or sends an [updateOne](/docs/api.html#document_Document-updateOne) operation **only** with the modifications to the database, it does not replace the whole document in the latter case.
  *
  * ####Example:
  *
diff --git a/lib/model.js b/lib/model.js
index cc9a7851232..784cfeb3683 100644
--- a/lib/model.js
+++ b/lib/model.js
@@ -415,7 +415,8 @@ function generateVersionError(doc, modifiedPaths) {
 }
 
 /**
- * Saves this document.
+ * Saves this document by inserting a new document into the database if [document.isNew](/docs/api.html#document_Document-isNew) is `true`,
+ * or sends an [updateOne](/docs/api.html#document_Document-updateOne) operation **only** with the modifications to the database, it does not replace the whole document in the latter case.
  *
  * ####Example:
  *