diff --git a/src/main/clojure/cljs/core/async/impl/ioc_macros.clj b/src/main/clojure/cljs/core/async/impl/ioc_macros.clj
index 7bd63c27..e3ae7c35 100644
--- a/src/main/clojure/cljs/core/async/impl/ioc_macros.clj
+++ b/src/main/clojure/cljs/core/async/impl/ioc_macros.clj
@@ -306,6 +306,16 @@
                       ~STATE-IDX :finished)
            nil))))
 
+(defrecord Set! [field object val]
+  IInstruction
+  (reads-from [this] [object val])
+  (writes-to [this] [(:id this)])
+  (block-references [this] [])
+  IEmittableInstruction
+  (emit-instruction [this state-sym]
+    `[~(:id this)
+      (set! (~field ~object) ~val)]))
+
 (defrecord CondBr [test then-block else-block]
   IInstruction
   (reads-from [this] [test])
@@ -396,6 +406,14 @@
       ret-id (add-instruction (->Const ::value))]
      ret-id)))
 
+(defmethod sexpr-to-ssa 'set!
+  [[_ [field obj] val]]
+  (gen-plan
+   [obj-id (item-to-ssa obj)
+    val-id (item-to-ssa val)
+    ret-id (add-instruction (->Set! field obj-id val-id))]
+   ret-id))
+
 (defmethod sexpr-to-ssa 'do
   [[_ & body]]
   (gen-plan
diff --git a/src/test/cljs/cljs/core/async/runner_tests.cljs b/src/test/cljs/cljs/core/async/runner_tests.cljs
index 3dfd4738..7151b4a2 100644
--- a/src/test/cljs/cljs/core/async/runner_tests.cljs
+++ b/src/test/cljs/cljs/core/async/runner_tests.cljs
@@ -88,6 +88,10 @@
                (pause x))
              42)))
 
+  (testing "set!"
+    (let [x (js-obj)]
+      (runner (set! (.-foo x) "bar"))))
+
   (testing "keywords as functions"
     (is (= :bar
            (runner (:foo (pause {:foo :bar}))))))