diff --git a/src/rss_thread_watch/utils.clj b/src/rss_thread_watch/utils.clj
index fa95d4f..13944fd 100644
--- a/src/rss_thread_watch/utils.clj
+++ b/src/rss_thread_watch/utils.clj
@@ -9,6 +9,18 @@
   [pred coll]
    (keep-indexed #(when (pred %2) %1) coll))
 
+(defn map-deep-merge-missing
+  "Merges two maps but only keys missing from first map"
+  [m1 m2]
+  (into m1
+        (for [k (keys m2)]
+          (let [val1 (get m1 k)
+                val2 (get m2 k)]
+            (if (and (map? val1)
+                     (map? val2))
+              {k (map-deep-merge-missing val1 val2)}
+              {k (nil?-else val2 val1)})))))
+
 ;; ===== Macros =====
 (defmacro nil?-else
   "Return x unless it's nil, the return y"