diff --git a/src/main/frontend/util.cljc b/src/main/frontend/util.cljc
index 5b35d682a2..9158c3e7eb 100644
--- a/src/main/frontend/util.cljc
+++ b/src/main/frontend/util.cljc
@@ -481,9 +481,8 @@
 #?(:cljs
    (defn distinct-by-last-wins
      [f col]
-     (if (sequential? col)
-       (reverse (distinct-by f (reverse col)))
-       (distinct-by f col))))
+     {:pre [(sequential? col)]}
+     (reverse (distinct-by f (reverse col)))))
 
 (defn get-git-owner-and-repo
   [repo-url]