diff --git a/src/rustint/core.clj b/src/rustint/core.clj
index a707257..5f78f62 100644
--- a/src/rustint/core.clj
+++ b/src/rustint/core.clj
@@ -2197,7 +2197,7 @@
             (list (clojure.string/join
               (interleave
                 (clojure.string/split (first args) #"\{:?(\.\d+)?\}")
-                (into '("") clojure-fspecifiers)
+                (concat clojure-fspecifiers '(""))
               )
             ))
           )