diff --git a/assemble.rkt b/assemble.rkt
index 7c3e7b4..54ccd85 100644
--- a/assemble.rkt
+++ b/assemble.rkt
@@ -238,7 +238,7 @@ EOF
      (format "return ~a();"
              (assemble-location (GotoStatement-target stmt)))]
     [(PushControlFrame? stmt)
-     (format "MACHINE.control.push(~a);" (PushControlFrame-label stmt))]
+     (format "MACHINE.control.push(new Frame(~a));" (PushControlFrame-label stmt))]
     [(PopControlFrame? stmt)
      "MACHINE.control.pop();"]
     [(PushEnvironment? stmt)
@@ -356,8 +356,9 @@ EOF
              (symbol->string (CheckToplevelBound!-name op)))]
     
     [(CheckClosureArity!? op)
-     ;; fixme
-     (error 'assemble-op-statement)]
+     (format "if (! (MACHINE.proc instanceof Closure && MACHINE.proc.arity === ~a)) { if (! (MACHINE.proc instanceof Closure)) { throw new Error(\"not a closure\"); } else { throw new Error(\"arity failure\"); } }"
+             (CheckClosureArity!-arity op)
+             )]
     
     [(ExtendEnvironment/Prefix!? op)
      (let: ([names : (Listof Symbol) (ExtendEnvironment/Prefix!-names op)])
diff --git a/test-assemble.rkt b/test-assemble.rkt
index d3b1910..96cb826 100644
--- a/test-assemble.rkt
+++ b/test-assemble.rkt
@@ -227,6 +227,49 @@
       "function,true")
 
 
+;; check-closure-arity.  This should succeed.
+(void (E-many (list (make-GotoStatement (make-Label 'afterLambdaBody))
+                    
+                    'closureStart
+                    (make-PerformStatement (make-InstallClosureValues!))
+                    (make-GotoStatement (make-Label 'theEnd))
+
+                    'afterLambdaBody
+                    (make-PushEnvironment 2)
+                    (make-AssignImmediateStatement (make-EnvLexicalReference 0)
+                                                   (make-Const "hello"))
+                    (make-AssignImmediateStatement (make-EnvLexicalReference 1)
+                                                   (make-Const "world"))
+                    (make-AssignPrimOpStatement 'proc (make-MakeCompiledProcedure 'closureStart 5 
+                                                                                  (list (make-EnvLexicalReference 0)
+                                                                                        (make-EnvLexicalReference 1))))
+                    (make-PopEnvironment 2 0)
+                    (make-PerformStatement (make-CheckClosureArity! 5)))))
+
+;; this should fail, since the check is for 1, but the closure expects 5.
+(let/ec return
+  (with-handlers ([void
+                   (lambda (exn) (return))])
+    (E-many (list (make-GotoStatement (make-Label 'afterLambdaBody))
+                  
+                  'closureStart
+                  (make-PerformStatement (make-InstallClosureValues!))
+                  (make-GotoStatement (make-Label 'theEnd))
+                  
+                  'afterLambdaBody
+                  (make-PushEnvironment 2)
+                  (make-AssignImmediateStatement (make-EnvLexicalReference 0)
+                                                 (make-Const "hello"))
+                  (make-AssignImmediateStatement (make-EnvLexicalReference 1)
+                                                 (make-Const "world"))
+                  (make-AssignPrimOpStatement 'proc (make-MakeCompiledProcedure 'closureStart 5 
+                                                                                (list (make-EnvLexicalReference 0)
+                                                                                      (make-EnvLexicalReference 1))))
+                  (make-PopEnvironment 2 0)
+                  (make-PerformStatement (make-CheckClosureArity! 1)))))
+  (error 'expected-failure))
+
+