--- a/js/src/ion/IonBuilder.cpp
+++ b/js/src/ion/IonBuilder.cpp
@@ -550,16 +550,19 @@ IonBuilder::inspectOpcode(JSOp op)
         return jsop_bitop(op);
 
       case JSOP_ADD:
       case JSOP_SUB:
       case JSOP_MUL:
       case JSOP_DIV:
       	return jsop_binary(op);
 
+      case JSOP_POS:
+        return jsop_pos();
+
       case JSOP_NEG:
         return jsop_neg();
 
       case JSOP_AND:
       case JSOP_OR:
         return jsop_andor(op);
 
       case JSOP_LOCALINC:
@@ -1949,16 +1952,31 @@ IonBuilder::jsop_binary(JSOp op)
 {
     MDefinition *right = current->pop();
     MDefinition *left = current->pop();
 
     return jsop_binary(op, left, right);
 }
 
 bool
+IonBuilder::jsop_pos()
+{
+    TypeOracle::Unary types = oracle->unaryOp(script, pc);
+    MDefinition *value = current->pop();
+    MInstruction *ins;
+    if (types.rval == MIRType_Int32)
+        ins = MToInt32::New(value);
+    else
+        ins = MToDouble::New(value);
+    current->add(ins);
+    current->push(ins);
+    return true;
+}
+
+bool
 IonBuilder::jsop_neg()
 {
     // Since JSOP_NEG does not use a slot, we cannot push the MConstant.
     // The MConstant is therefore passed to JSOP_MUL without slot traffic.
     MConstant *negator = MConstant::New(Int32Value(-1));
     current->add(negator);
 
     MDefinition *right = current->pop();

--- a/js/src/ion/IonBuilder.h
+++ b/js/src/ion/IonBuilder.h
@@ -268,16 +268,17 @@ class IonBuilder : public MIRGenerator
     void initParameters();
     void rewriteParameters();
     bool pushConstant(const Value &v);
     bool pushTypeBarrier(MInstruction *ins, types::TypeSet *actual, types::TypeSet *observed);
     bool jsop_bitnot();
     bool jsop_bitop(JSOp op);
     bool jsop_binary(JSOp op);
     bool jsop_binary(JSOp op, MDefinition *left, MDefinition *right);
+    bool jsop_pos();
     bool jsop_neg();
     bool jsop_notearg();
     bool jsop_call(uint32 argc);
     bool jsop_ifeq(JSOp op);
     bool jsop_andor(JSOp op);
     bool jsop_dup2();
     bool jsop_incslot(JSOp op, uint32 slot);
     bool jsop_localinc(JSOp op);

new file mode 100644
--- /dev/null
+++ b/js/src/jit-test/tests/ion/testPos.js
@@ -0,0 +1,32 @@
+// vim: set ts=4 sw=4 tw=99 et:
+function f_int(x) {
+    return +x;
+}
+
+function f_double(x) {
+    return +x;
+}
+
+for (var i = 0; i < 1000; i++) {
+    assertEq(f_int(0), 0);
+    assertEq(f_int(1), 1);
+    assertEq(f_int(-1), -1);
+    assertEq(f_int(-2147483648), -2147483648);
+    assertEq(f_int(2147483647), 2147483647);
+}
+
+for (var i = 0; i < 1000; i++) {
+    assertEq(f_double(0.0), 0.0);
+    assertEq(f_double(1.0), 1.0);
+    assertEq(f_double(-1.0), -1.0);
+    assertEq(f_double(-2.147483648), -2.147483648);
+    assertEq(f_double(2.147483647), 2.147483647);
+}
+
+for (var i = 0; i < 1000; i++) {
+    assertEq(f_double("0.0"), 0.0);
+    assertEq(f_double("1.0"), 1.0);
+    assertEq(f_double("-1.0"), -1.0);
+    assertEq(f_double("-2.147483648"), -2.147483648);
+    assertEq(f_double("2.147483647"), 2.147483647);
+}