diff --git a/src/main/cljs/cljs/core.cljs b/src/main/cljs/cljs/core.cljs
index ae991f0a6..993a5d5fe 100644
--- a/src/main/cljs/cljs/core.cljs
+++ b/src/main/cljs/cljs/core.cljs
@@ -13142,7 +13142,7 @@ reduces them without incurring seq initialization"
 (set! (. SetLite -EMPTY) (SetLite. nil (. HashMapLite -EMPTY) empty-unordered-hash))
 
 (defn set-lite
-  ":lite-mode version of set, not intended ot be used directly."
+  ":lite-mode version of set, not intended to be used directly."
   [coll]
   (if (set? coll)
     (-with-meta coll nil)
@@ -13151,5 +13151,23 @@ reduces them without incurring seq initialization"
         #{}
         (loop [in in out (. SetLite -EMPTY)]
           (if-not (nil? in)
-            (recur (next in) (-conj out (first in)))
+            (recur (next in) (conj out (first in)))
+            out))))))
+
+(defn set-lite-check
+  ":lite-mode version of set with check, not intended to be used directly."
+  [coll]
+  (if (set? coll)
+    (-with-meta coll nil)
+    (let [in (seq coll)]
+      (if (nil? in)
+        #{}
+        (loop [in in out (. SetLite -EMPTY) i 0]
+          (if-not (nil? in)
+            (let [x    (first in)
+                  out' (conj out x)
+                  i'   (inc i)]
+              (if-not (== i' (count out'))
+                (throw (js/Error. (str_ "Duplicate key: " x)))
+                (recur (next in) out' i')))
             out))))))
diff --git a/src/main/clojure/cljs/compiler.cljc b/src/main/clojure/cljs/compiler.cljc
index 1fbf54ec2..4bc7ea215 100644
--- a/src/main/clojure/cljs/compiler.cljc
+++ b/src/main/clojure/cljs/compiler.cljc
@@ -614,12 +614,17 @@
     (emits "new cljs.core.PersistentHashSet(null, new cljs.core.PersistentArrayMap(null, " (count items) ", ["
       (comma-sep (interleave items (repeat "null"))) "], null), null)")
 
-    :else (emits "cljs.core.PersistentHashSet.createAsIfByAssoc([" (comma-sep items) "])")))
+    :else (emits "cljs.core.PersistentHashSet.createWithCheck([" (comma-sep items) "])")))
 
 (defn emit-lite-set [items comma-sep distinct-constants?]
-  (if (empty? items)
+  (cond
+    (empty? items)
     (emits "cljs.core.SetLite.EMPTY")
-    (emits "cljs.core.set_lite([" (comma-sep items) "])")))
+
+    (distinct-constants? items)
+    (emits "cljs.core.set_lite([" (comma-sep items) "])")
+
+    :else (emits "cljs.core.set_lite_check([" (comma-sep items) "])")))
 
 (defmethod emit* :set
   [{:keys [items env]}]
diff --git a/src/test/cljs/cljs/core_test.cljs b/src/test/cljs/cljs/core_test.cljs
index 01f6f0b52..8bff60d3b 100644
--- a/src/test/cljs/cljs/core_test.cljs
+++ b/src/test/cljs/cljs/core_test.cljs
@@ -824,9 +824,6 @@
 (def some-x 1)
 (def some-y 1)
 
-(deftest test-583
-  (is (= (count #{some-x some-y}) 1)))
-
 (deftest test-584
   (is (= (count {some-x :foo some-y :bar}) 1)))
 
@@ -2012,3 +2009,7 @@
 (deftest test-instance-method-new
   (is (= ["FOO" "BAR" "BAZ"]
          (map String/.toUpperCase ["foo" "bar" "baz"]))))
+
+(deftest test-cljs-3415
+  (let [a 1 b 1]
+    (is (thrown? js/Error #{a b}))))
\ No newline at end of file