--- a/js/src/ion/IonBuilder.cpp
+++ b/js/src/ion/IonBuilder.cpp
@@ -398,16 +398,20 @@ IonBuilder::inspectOpcode(JSOp op)
         return pushConstant(Int32Value(0));
 
       case JSOP_ONE:
         return pushConstant(Int32Value(1));
 
       case JSOP_NULL:
         return pushConstant(NullValue());
 
+      case JSOP_VOID:
+        current->pop();
+        return pushConstant(UndefinedValue());
+
       case JSOP_FALSE:
         return pushConstant(BooleanValue(false));
 
       case JSOP_TRUE:
         return pushConstant(BooleanValue(true));
 
       case JSOP_GETARG:
         current->pushArg(GET_SLOTNO(pc));

new file mode 100644
--- /dev/null
+++ b/js/src/jit-test/tests/ion/void.js
@@ -0,0 +1,6 @@
+function f() {
+    var b, c;
+    var a = void ( b = 5, c = 7 );    
+    return a;
+}
+assertEq(typeof f(), "undefined")