diff --git a/compiler/il-structs.rkt b/compiler/il-structs.rkt
index 3301803..e9b0537 100644
--- a/compiler/il-structs.rkt
+++ b/compiler/il-structs.rkt
@@ -201,11 +201,15 @@
   #:transparent)
 
 
+;; FIXME: it would be nice if I can reduce AssignImmediate and
+;; AssignPrimOp into a single Assign statement, but I run into major
+;; issues with Typed Racket taking minutes to compile.  So we're
+;; running into some kind of degenerate behavior.
 (define-struct: AssignImmediate ([target : Target]
-                                          [value : OpArg])
+                                 [value : OpArg])
   #:transparent)
 (define-struct: AssignPrimOp ([target : Target]
-                                       [op : PrimitiveOperator])
+                              [op : PrimitiveOperator])
   #:transparent)
 
 
@@ -328,8 +332,6 @@
 (define-struct: ApplyPrimitiveProcedure () #:transparent)
 
 
-
-
 (define-struct: MakeBoxedEnvironmentValue ([depth : Natural])
   #:transparent)
 
diff --git a/js-assembler/assemble-open-coded.rkt b/js-assembler/assemble-open-coded.rkt
index b6f2ffe..0213c40 100644
--- a/js-assembler/assemble-open-coded.rkt
+++ b/js-assembler/assemble-open-coded.rkt
@@ -11,6 +11,9 @@
 
 (provide open-code-kernel-primitive-procedure)
 
+;; Conservative estimate: JavaScript evaluators don't like to eat
+;; more than some number of arguments at once.
+(define MAX-JAVASCRIPT-ARGS-AT-ONCE 100)
 
 
 (: open-code-kernel-primitive-procedure (CallKernelPrimitiveProcedure Blockht -> String))
@@ -33,14 +36,18 @@
           [(+)
            (cond [(empty? checked-operands)
                   (assemble-numeric-constant 0)]
+                 [(< (length operands) MAX-JAVASCRIPT-ARGS-AT-ONCE)
+                  (format "RT.checkedAdd(M, ~a)" (string-join operands ","))]
                  [else
-                  (assemble-binop-chain "plt.baselib.numbers.add" checked-operands)])]
+                  (format "RT.checkedAddSlowPath(M, [~a])" (string-join operands ","))])]
           
           [(-)
            (cond [(empty? (rest checked-operands))
                   (format "RT.checkedNegate(M, ~a)" (first operands))]
+                 [(< (length operands) MAX-JAVASCRIPT-ARGS-AT-ONCE)
+                  (format "RT.checkedSub(M, ~a)" (string-join operands ","))]
                  [else
-                  (assemble-binop-chain "plt.baselib.numbers.subtract" checked-operands)])]
+                  (format "RT.checkedSubSlowPath(M, [~a])" (string-join operands ","))])]
           
           [(*)
            (cond [(empty? checked-operands)
@@ -133,8 +140,6 @@
 
 
 
-
-
 (: assemble-boolean-chain (String (Listof String) -> String))
 (define (assemble-boolean-chain rator rands)
   (string-append "("
diff --git a/js-assembler/runtime-src/runtime.js b/js-assembler/runtime-src/runtime.js
index 4f93f08..d849f21 100644
--- a/js-assembler/runtime-src/runtime.js
+++ b/js-assembler/runtime-src/runtime.js
@@ -833,6 +833,70 @@
             testArgument(M, 'number', isNumber, n, 0, '-'));
     };
 
+    var checkedAdd = function(M) {
+        var i;
+        var sum = 0;
+        for (i = 1; i < arguments.length; i++) {
+            if (typeof(arguments[i] === 'number')) {
+                sum += arguments[i];
+                if (sum < -9e15 || sum > 9e15) {
+                    return checkedAddSlowPath(M, Array.prototype.slice.call(arguments, 1));
+                }
+            } else {
+                return checkedAddSlowPath(M, Array.prototype.slice.call(arguments, 1));
+            }
+        }
+        return sum;
+    };
+
+    var checkedAddSlowPath = function(M, args) {
+        var i;
+        var sum = 0;
+        for (i = 0; i < args.length; i++) {
+            if (! isNumber(args[i])) {
+                raiseArgumentTypeError(M, '+', 'number', i, args[i]);
+            }
+            sum = plt.baselib.numbers.add(sum, args[i]);
+        }
+        return sum;
+    };
+
+    var checkedSub = function(M) {
+        // Assumption: at least two arguments to subtract.
+        var i;
+        if (typeof(arguments[1]) !== 'number') {
+            return checkedSubSlowPath(M, Array.prototype.slice.call(arguments, 1));
+        }
+        var sum = arguments[1];
+        for (i = 2; i < arguments.length; i++) {
+            if (typeof(arguments[i] === 'number')) {
+                sum -= arguments[i];
+                if (sum < -9e15 || sum > 9e15) {
+                    return checkedSubSlowPath(M, Array.prototype.slice.call(arguments, 1));
+                }
+            } else {
+                return checkedSubSlowPath(M, Array.prototype.slice.call(arguments, 1));
+            }
+        }
+        return sum;
+    };
+
+    var checkedSubSlowPath = function(M, args) {
+        var i;
+        if (! isNumber(args[0])) {
+            raiseArgumentTypeError(M, '-', 'number', 0, args[0]);
+        }
+        var sum = args[0];
+        for (i = 1; i < args.length; i++) {
+            if (! isNumber(args[i])) {
+                raiseArgumentTypeError(M, '-', 'number', i, args[i]);
+            }
+            sum = plt.baselib.numbers.sub(sum, args[i]);
+        }
+        return sum;
+    };
+
+
     var checkedCar = function(M, v) {
         if (isPair(v)) { return v.first; }
         raiseArgumentTypeError(M, 'car', 'pair', 0, v);
@@ -983,6 +1047,10 @@
     exports['checkedAdd1'] = checkedAdd1;
     exports['checkedSub1'] = checkedSub1;
     exports['checkedNegate'] = checkedNegate;
+    exports['checkedAdd'] = checkedAdd;
+    exports['checkedAddSlowPath'] = checkedAddSlowPath;
+    exports['checkedSub'] = checkedSub;
+    exports['checkedSubSlowPath'] = checkedSubSlowPath;
     exports['checkedCar'] = checkedCar;
     exports['checkedCdr'] = checkedCdr;
 }(this.plt, this.plt.baselib));
\ No newline at end of file
diff --git a/version.rkt b/version.rkt
index b83c1d9..fd81eb7 100644
--- a/version.rkt
+++ b/version.rkt
@@ -7,4 +7,4 @@
 (provide version)
 (: version String)
 
-(define version "1.150")
+(define version "1.154")