diff --git a/js/src/builtin/Array.js b/js/src/builtin/Array.js
index 69e1ef7b0c3..e125aecd430 100644
--- a/js/src/builtin/Array.js
+++ b/js/src/builtin/Array.js
@@ -715,7 +715,7 @@ function ArrayMapPar(func, mode) {
     UnsafePutElements(buffer, i, func(self[i], i, self));
   return buffer;
 
-  function mapThread(warmup) {
+  function mapThread(_, warmup) {
     var sliceId;
     while (GET_SLICE(slicesInfo, sliceId)) {
       var indexStart = SLICE_START(slicesInfo, sliceId);
@@ -770,7 +770,7 @@ function ArrayReducePar(func, mode) {
     accumulator = func(accumulator, self[i]);
   return accumulator;
 
-  function reduceThread(warmup) {
+  function reduceThread(_, warmup) {
     var sliceId;
     while (GET_SLICE(slicesInfo, sliceId)) {
       var indexStart = SLICE_START(slicesInfo, sliceId);
@@ -867,7 +867,7 @@ function ArrayScanPar(func, mode) {
    *
    * Read on in phase2 to see what we do next!
    */
-  function phase1(warmup) {
+  function phase1(_, warmup) {
     var sliceId;
     while (GET_SLICE(slicesInfo, sliceId)) {
       var indexStart = SLICE_START(slicesInfo, sliceId);
@@ -919,7 +919,7 @@ function ArrayScanPar(func, mode) {
    * result is [(A+B+C)+D, (A+B+C)+(D+E), (A+B+C)+(D+E+F)]. Again I
    * am using parentheses to clarify how these results were reduced.
    */
-  function phase2(warmup) {
+  function phase2(_, warmup) {
     var sliceId;
     while (GET_SLICE(slicesInfo, sliceId)) {
       var indexPos = SLICE_START(slicesInfo, sliceId);
@@ -1087,7 +1087,7 @@ function ArrayFilterPar(func, mode) {
    * time. When we finish a chunk, we record our current count and
    * the next chunk sliceId, lest we should bail.
    */
-  function findSurvivorsThread(warmup) {
+  function findSurvivorsThread(_, warmup) {
     var sliceId;
     while (GET_SLICE(slicesInfo, sliceId)) {
       var count = 0;
@@ -1112,7 +1112,7 @@ function ArrayFilterPar(func, mode) {
     }
   }
 
-  function copySurvivorsThread(warmup) {
+  function copySurvivorsThread(_, warmup) {
     var sliceId;
     while (GET_SLICE(slicesInfo, sliceId)) {
       // Copies the survivors from this slice into the correct position.
@@ -1214,7 +1214,7 @@ function ArrayStaticBuildPar(length, func, mode) {
     UnsafePutElements(buffer, i, func(i));
   return buffer;
 
-  function constructThread(warmup) {
+  function constructThread(_, warmup) {
     var sliceId;
     while (GET_SLICE(slicesInfo, sliceId)) {
       var indexStart = SLICE_START(slicesInfo, sliceId);
diff --git a/js/src/vm/ForkJoin.cpp b/js/src/vm/ForkJoin.cpp
index 29823012909..1856328137f 100644
--- a/js/src/vm/ForkJoin.cpp
+++ b/js/src/vm/ForkJoin.cpp
@@ -173,11 +173,12 @@ ExecuteSequentially(JSContext *cx, HandleValue funVal)
 {
     FastInvokeGuard fig(cx, funVal);
     InvokeArgs &args = fig.args();
-    if (!args.init(1))
+    if (!args.init(2))
         return false;
     args.setCallee(funVal);
     args.setThis(UndefinedValue());
-    args[0].setBoolean(!!cx->runtime()->forkJoinWarmup);
+    args[0].setInt32(0); // always worker 0 in seq
+    args[1].setBoolean(!!cx->runtime()->forkJoinWarmup);
     return fig.invoke(cx);
 }
 
@@ -1520,9 +1521,10 @@ ForkJoinShared::executePortion(PerThreadData *perThread, uint32_t workerId)
         cx.bailoutRecord->setCause(ParallelBailoutMainScriptNotPresent);
         setAbortFlagAndTriggerOperationCallback(false);
     } else {
-        ParallelIonInvoke<2> fii(cx_->runtime(), fun_, 1);
+        ParallelIonInvoke<2> fii(cx_->runtime(), fun_, 2);
 
-        fii.args[0] = BooleanValue(false);
+        fii.args[0] = Int32Value(workerId);
+        fii.args[1] = BooleanValue(false);
 
         bool ok = fii.invoke(perThread);
         JS_ASSERT(ok == !cx.bailoutRecord->topScript);