diff --git a/src/loom/derived.cljc b/src/loom/derived.cljc
index c5bc7ed..71f1008 100644
--- a/src/loom/derived.cljc
+++ b/src/loom/derived.cljc
@@ -12,9 +12,12 @@
   edge [uu, vv] is an edge in the resulting graph iff g has an edge [u, v] such
   that [uu, vv] = [(f u), (f v)]."
   [f g]
-  (-> (if (directed? g) (digraph) (graph))
-      (add-nodes* (map f (nodes g)))
-      (add-edges* (map #(map f %) (edges g)))))
+  (let [mapped-nodes (into {} (map (fn [n]
+                                     [n (f n)])
+                                   (nodes g)))]
+    (-> (if (directed? g) (digraph) (graph))
+        (add-nodes* (map mapped-nodes (nodes g)))
+        (add-edges* (map #(map mapped-nodes %) (edges g))))))
 
 (defn subgraph-reachable-from
   "Returns a subgraph of the given graph which contains all nodes and edges that
diff --git a/test/loom/test/derived.cljc b/test/loom/test/derived.cljc
index c6dce6e..9fcb1a1 100644
--- a/test/loom/test/derived.cljc
+++ b/test/loom/test/derived.cljc
@@ -1,7 +1,7 @@
 (ns loom.test.derived
   (:require [loom.derived :refer [mapped-by nodes-filtered-by edges-filtered-by
                                   subgraph-reachable-from bipartite-subgraph]]
-            [loom.graph :refer (graph digraph edges)]
+            [loom.graph :refer (graph digraph edges nodes)]
             [loom.alg :refer (eql?)]
             #?@(:clj [[clojure.test :refer :all]]
                 :cljs [cljs.test]))
@@ -19,6 +19,10 @@
                    (mapped-by inc g))
         true (eql? (graph [2 0] [2 1] [0 1] 2)
                    (mapped-by #(mod % 3) g))
+
+        (count (nodes g)) (let [counter (atom 0)]
+                            (count (nodes (mapped-by (fn [_] (swap! counter inc))
+                                                     g))))
         ;; digraph
         true (eql? dg
                    (mapped-by identity dg))