diff --git a/bootstrapped-primitives.rkt b/bootstrapped-primitives.rkt
index 241d12b..23ac492 100644
--- a/bootstrapped-primitives.rkt
+++ b/bootstrapped-primitives.rkt
@@ -43,7 +43,8 @@
                                                                 1 ;; the continuation consumes a single value
                                                                 (list 0 1)
                                                                 'call/cc))
-       ,(make-PopEnvironment 2 0)))
+       ,(make-PopEnvironment 2 0)
+       ,(make-AssignImmediateStatement 'argcount (make-Const 1))))
     
     ;; Finally, do a tail call into f.
     (compile-general-procedure-call '()
diff --git a/compile.rkt b/compile.rkt
index fd29df4..4b9043b 100644
--- a/compile.rkt
+++ b/compile.rkt
@@ -468,6 +468,9 @@
          empty-instruction-sequence)
      proc-code
      (juggle-operands operand-codes)
+     (make-instruction-sequence `(,(make-AssignImmediateStatement 
+                                    'argcount
+                                    (make-Const (length (App-operands exp))))))
      (compile-general-procedure-call cenv 
                                      (length extended-cenv)
                                      (length (App-operands exp))
@@ -784,6 +787,7 @@
                                                           ->
                                                           InstructionSequence))
 ;; Assumes the procedure value has been loaded into the proc register.
+;; and the # of values passed in has been written into argcount.
 ;; n is the number of arguments passed in.
 ;; cenv is the compile-time enviroment before arguments have been shifted in.
 ;; extended-cenv is the compile-time environment after arguments have been shifted in.
@@ -804,8 +808,7 @@
                ;; Compiled branch
                (LabelLinkage-label compiled-branch)
                (make-instruction-sequence
-                `(,(make-AssignImmediateStatement 'val (make-Const number-of-arguments))
-                  ,(make-PerformStatement (make-CheckClosureArity! (make-Reg 'val)))))
+                `(,(make-PerformStatement (make-CheckClosureArity! (make-Reg 'argcount)))))
                (compile-procedure-application extended-cenv-length
                                               (make-Reg 'val)
                                               number-of-arguments 
@@ -1189,6 +1192,8 @@
      target]
     [(eq? target 'proc)
      target]
+    [(eq? target 'argcount)
+     target]
     [(EnvLexicalReference? target)
      (make-EnvLexicalReference (+ n (EnvLexicalReference-depth target))
                                (EnvLexicalReference-unbox? target))]
diff --git a/il-structs.rkt b/il-structs.rkt
index fa7f418..f180b48 100644
--- a/il-structs.rkt
+++ b/il-structs.rkt
@@ -11,7 +11,7 @@
 ;; Registers of the machine:
 
 (define-type StackRegisterSymbol (U 'control 'env))
-(define-type AtomicRegisterSymbol (U 'val 'proc))
+(define-type AtomicRegisterSymbol (U 'val 'proc 'argcount))
 (define-type RegisterSymbol (U StackRegisterSymbol AtomicRegisterSymbol))
 
 (define-predicate AtomicRegisterSymbol? AtomicRegisterSymbol)