diff --git a/lib/mongoid_paperclip.rb b/lib/mongoid_paperclip.rb
index 90787c5..67c8be2 100644
--- a/lib/mongoid_paperclip.rb
+++ b/lib/mongoid_paperclip.rb
@@ -6,8 +6,8 @@
   case id = attachment.instance.id
   when Integer
     ("%09d".freeze % id).scan(/\d{3}/).join("/".freeze)
-  when String
-    id.scan(/.{4}/).join("/".freeze)
+  when String, BSON::ObjectId
+    id.to_s.scan(/.{4}/).join("/".freeze)
   else
     nil
   end
diff --git a/spec/mongoid-paperclip_spec.rb b/spec/mongoid-paperclip_spec.rb
index 626eb14..99cdaa4 100644
--- a/spec/mongoid-paperclip_spec.rb
+++ b/spec/mongoid-paperclip_spec.rb
@@ -27,6 +27,12 @@
     it "stores fingerprint" do
       expect(user.avatar_fingerprint).to eq("2584a801e588b3fcf4aa074efff77e30")
     end
+
+    it "interpolates path and url properly" do
+      id_partition = user.id.to_s.scan(/.{4}/).join("/")
+      expect(user.avatar.url).to eq("/system/users/#{id_partition}/avatar-original.png?#{Time.now.to_i}")
+      expect(user.avatar.path).to eq("#{__dir__}/public/system/users/#{id_partition}/avatar-original.png")
+    end
   end
 
   describe "multiple attachments" do
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 6021228..09cff1e 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -22,7 +22,7 @@ class User
   include Mongoid::Document
   include Mongoid::Paperclip
 
-  has_mongoid_attached_file :avatar
+  has_mongoid_attached_file :avatar, url: "/system/:class/:id_partition/:basename-:style.:extension"
   validates_attachment_content_type :avatar, content_type: /\Aimage\/.*\Z/
 end