diff --git a/js-assembler/assemble-open-coded.rkt b/js-assembler/assemble-open-coded.rkt
index 1ec42dd..f3fe0b7 100644
--- a/js-assembler/assemble-open-coded.rkt
+++ b/js-assembler/assemble-open-coded.rkt
@@ -52,21 +52,11 @@
            (assemble-binop-chain "plt.baselib.numbers.divide" checked-operands)]
 
           [(add1)
-           (string-append
-            (format "(typeof(~a)==='number'&&(~a)<9E15?(~a)+1"
-                    (first operands) (first operands) (first operands))
-            ":"
-            (format "RT.checkedAdd1(M, ~a)" (first operands))
-            ")")]
-
+           (format "RT.checkedAdd1(M, ~a)" (first operands))]
           
           [(sub1)
-           (string-append
-            (format "(typeof(~a)==='number'&&(~a)>-9E15?(~a)-1"
-                    (first operands) (first operands) (first operands))
-            ":"
-            (format "RT.checkedSub1(M, ~a)" (first operands))
-            ")")]
+           (format "RT.checkedSub1(M, ~a)" (first operands))]
+
           [(<)
            (assemble-boolean-chain "plt.baselib.numbers.lessThan" checked-operands)]
 
@@ -88,13 +78,13 @@
                    (second checked-operands))]
 
           [(car)
-           (format "(~a).first" (first checked-operands))]
+           (format "RT.checkedCar(M, ~a)" (first operands))]
 
           [(caar)
            (format "(~a).first.first" (first checked-operands))]
           
           [(cdr)
-           (format "(~a).rest" (first checked-operands))]
+           (format "RT.checkedCdr(M, ~a)" (first operands))]
           
           [(list)
            (let loop ([checked-operands checked-operands])
diff --git a/js-assembler/runtime-src/runtime.js b/js-assembler/runtime-src/runtime.js
index 18255e6..9f17547 100644
--- a/js-assembler/runtime-src/runtime.js
+++ b/js-assembler/runtime-src/runtime.js
@@ -806,16 +806,28 @@
 
     //////////////////////////////////////////////////////////////////////
     var checkedAdd1 = function(M, n) {
+        if (typeof(n) === 'number' && n < 9e15) { return n+1; }
         return plt.baselib.numbers.add(
             testArgument(M, 'number', isNumber, n, 0, 'add1'),
             1);
     };
 
     var checkedSub1 = function(M, n) {
+        if (typeof(n) === 'number' && n > -9e15) { return n-1; }
         return plt.baselib.numbers.subtract(
             testArgument(M, 'number', isNumber, n, 0, 'add1'),
             1);
     };
+    var checkedCar = function(M, v) {
+        if (isPair(v)) { return v.first; }
+        raiseArgumentTypeError(M, 'car', 'pair', 0, v);
+    };
+
+    var checkedCdr = function(M, v) {
+        if (isPair(v)) { return v.rest; }
+        raiseArgumentTypeError(M, 'cdr', 'pair', 0, v);
+    };
+
 
 
 
@@ -957,4 +969,6 @@
 
     exports['checkedAdd1'] = checkedAdd1;
     exports['checkedSub1'] = checkedSub1;
+    exports['checkedCar'] = checkedCar;
+    exports['checkedCdr'] = checkedCdr;
 }(this.plt, this.plt.baselib));
\ No newline at end of file