diff --git a/compile.rkt b/compile.rkt
index 99d508c..d21a425 100644
--- a/compile.rkt
+++ b/compile.rkt
@@ -52,7 +52,9 @@
     [(LetVoid? exp)
      (compile-let-void exp cenv target linkage)]
     [(InstallValue? exp)
-     (compile-install-value exp cenv target linkage)]))
+     (compile-install-value exp cenv target linkage)]
+    [(BoxEnv? exp)
+     (compile-box-environment-value exp cenv target linkage)]))
 
 
 
@@ -513,6 +515,13 @@
 
 
 
+(: compile-box-environment-value (BoxEnv Natural Target Linkage -> InstructionSequence))
+(define (compile-box-environment-value exp cenv target linkage)
+   (append-instruction-sequences
+    (make-instruction-sequence 
+     `(,(make-AssignPrimOpStatement (make-EnvLexicalReference (BoxEnv-depth exp) #f)
+                                    (make-MakeBoxedEnvironmentValue (BoxEnv-depth exp)))))
+    (compile (BoxEnv-body exp) cenv target linkage)))
 
 
 (: append-instruction-sequences (InstructionSequence * -> InstructionSequence))
diff --git a/il-structs.rkt b/il-structs.rkt
index b045eb1..a368647 100644
--- a/il-structs.rkt
+++ b/il-structs.rkt
@@ -117,6 +117,7 @@
                                   MakeCompiledProcedure
                                   ApplyPrimitiveProcedure
                                   GetControlStackLabel
+                                  MakeBoxedEnvironmentValue
 
                                   CaptureEnvironment
                                   CaptureControl
@@ -150,6 +151,10 @@
 (define-struct: GetControlStackLabel ()
   #:transparent)
 
+(define-struct: MakeBoxedEnvironmentValue ([depth : Natural])
+  #:transparent)
+
+
 ;; Capture the current environment, skipping skip frames.
 (define-struct: CaptureEnvironment ([skip : Natural]))
 
diff --git a/simulator.rkt b/simulator.rkt
index d2756ad..c67b30f 100644
--- a/simulator.rkt
+++ b/simulator.rkt
@@ -314,7 +314,11 @@
                                                               (CaptureEnvironment-skip op))))]
           [(CaptureControl? op)
            (target-updater! m (make-CapturedControl (drop (machine-control m)
-                                                          (CaptureControl-skip op))))])))
+                                                          (CaptureControl-skip op))))]
+          [(MakeBoxedEnvironmentValue? op)
+           (target-updater! m (box (ensure-primitive-value
+                                    (env-ref m (MakeBoxedEnvironmentValue-depth op)))))])))
+
 
 
 
diff --git a/test-compiler.rkt b/test-compiler.rkt
index 0279dae..8528561 100644
--- a/test-compiler.rkt
+++ b/test-compiler.rkt
@@ -647,6 +647,22 @@
 	     
 
 
+(test '(begin (define counter 0)
+              (set! counter (add1 counter))
+              counter)
+      1)
+
+(test '(begin (define x 16)
+              (define (f x)
+                (set! x (add1 x))
+                x)
+              (list (f 3)
+                    (f 4)
+                    x))
+      (list 4 5 16))
+      
+
+
 #;(test (read (open-input-file "tests/conform/program0.sch"))
       (port->string (open-input-file "tests/conform/expected0.txt")))