diff --git a/README.md b/README.md
index ce88b8144..58aae65c2 100644
--- a/README.md
+++ b/README.md
@@ -267,8 +267,6 @@ Supported relations are:
  - belongsTo
  - belongsToMany
 
-*The belongsToMany relation will not use a pivot "table", but will push id's to a __related_ids__ attribute instead.*
-
 Example:
 
     use Jenssegers\Mongodb\Model as Eloquent;
@@ -295,6 +293,19 @@ And the inverse relation:
 
     }
 
+The belongsToMany relation will not use a pivot "table", but will push id's to a __related_ids__ attribute instead. This makes the second parameter for the belongsToMany method useless. If you want to define custom keys for your relation, set it to `null`:
+
+    use Jenssegers\Mongodb\Model as Eloquent;
+
+    class User extends Eloquent {
+
+        public function groups()
+        {
+            return $this->belongsToMany('Group', null, 'users', 'groups');
+        }
+
+    }
+
 Other relations are not yet supported, but may be added in the future. Read more about these relations on http://four.laravel.com/docs/eloquent#relationships
 
 ### Raw Expressions
diff --git a/tests/models/Group.php b/tests/models/Group.php
index 5332948d3..9e06f0773 100644
--- a/tests/models/Group.php
+++ b/tests/models/Group.php
@@ -9,6 +9,6 @@ class Group extends Eloquent {
 
 	public function users()
 	{
-		return $this->belongsToMany('User', 'test_collection', 'groups', 'users');
+		return $this->belongsToMany('User', null, 'groups', 'users');
 	}
 }
diff --git a/tests/models/User.php b/tests/models/User.php
index 5a8d352fe..56ef54b45 100644
--- a/tests/models/User.php
+++ b/tests/models/User.php
@@ -35,7 +35,7 @@ public function clients()
 
     public function groups()
     {
-        return $this->belongsToMany('Group', 'test_collection', 'users', 'groups');
+        return $this->belongsToMany('Group', null, 'users', 'groups');
     }
 
     /**