diff --git a/src/monger/util.clj b/src/monger/util.clj
index 2947b01..698251e 100644
--- a/src/monger/util.clj
+++ b/src/monger/util.clj
@@ -8,7 +8,7 @@
 ;; You must not remove this notice, or any other, from this software.
 
 (ns monger.util
-  (:import (java.security SecureRandom) (java.math BigInteger) (org.bson.types ObjectId) (com.mongodb DBObject)))
+  (:import (java.security SecureRandom) (java.math BigInteger) (org.bson.types ObjectId) (com.mongodb DBObject) (clojure.lang IPersistentMap) (java.util Map)))
 
 ;;
 ;; API
@@ -36,11 +36,16 @@
   `(binding [*ns* (the-ns ~ns)]
      ~@(map (fn [form] `(eval '~form)) body)))
 
-(defprotocol GetDBObjectId
-  (get-id  [input] "Returns object id"))
+(defprotocol GetDocumentId
+  (get-id  [input] "Returns document id"))
 
-(extend-protocol GetDBObjectId
+(extend-protocol GetDocumentId
   DBObject
   (get-id
    [^DBObject object]
-   (.get ^DBObject object "_id")))
\ No newline at end of file
+    (.get object "_id"))
+
+  IPersistentMap
+  (get-id
+    [^IPersistentMap object]
+    (or (:_id object) ("_id" object))))
diff --git a/test/monger/test/util.clj b/test/monger/test/util.clj
index a925041..4e3e0d2 100644
--- a/test/monger/test/util.clj
+++ b/test/monger/test/util.clj
@@ -5,9 +5,10 @@
 
 
 (deftest get-object-id
-  (let [id     ^ObjectId (monger.util/object-id)
-        input  ^DBObject (monger.conversion/to-db-object { :_id id })
-        output (monger.util/get-id input)]
-    (is (not (nil? output)))))
+  (let [clj-map   { :_id (monger.util/object-id) }
+        db-object ^DBObject (monger.conversion/to-db-object clj-map)
+        _id       (:_id clj-map)]
+    (is (= _id (monger.util/get-id clj-map)))
+    (is (= _id (monger.util/get-id db-object)))))