diff --git a/src/monger/json.clj b/src/monger/json.clj
new file mode 100644
index 0000000..780d681
--- /dev/null
+++ b/src/monger/json.clj
@@ -0,0 +1,8 @@
+(ns monger.json
+  (:import (org.bson.types ObjectId))
+  (:require [clojure.data.json :as json]))
+
+(extend-protocol json/Write-JSON
+  ObjectId
+  (write-json [^ObjectId object out escape-unicode?]
+    (json/write-json (.toString object) out escape-unicode?)))