diff --git a/src/harmony-math.js b/src/harmony-math.js
index e7afa4d607..298fa58cb2 100644
--- a/src/harmony-math.js
+++ b/src/harmony-math.js
@@ -175,10 +175,29 @@ function MathClz32(x) {
 
 
 // ES6 draft 09-27-13, section 20.2.2.9.
+// Cube root approximation, refer to: http://metamerist.com/cbrt/cbrt.htm
+// Using initial approximation adapted from Kahan's cbrt and 4 iterations
+// of Newton's method.
 function MathCbrt(x) {
-  return %Math_cbrt(TO_NUMBER_INLINE(x));
+  if (!IS_NUMBER(x)) x = NonNumberToNumber(x);
+  if (x == 0 || !NUMBER_IS_FINITE(x)) return x;
+  return x >= 0 ? CubeRoot(x) : -CubeRoot(-x);
 }
 
+macro NEWTON_ITERATION_CBRT(x, approx)
+  (1.0 / 3.0) * (x / (approx * approx) + 2 * approx);
+endmacro
+
+function CubeRoot(x) {
+  var approx_hi = MathFloor(%_DoubleHi(x) / 3) + 0x2A9F7893;
+  var approx = %_ConstructDouble(approx_hi, 0);
+  approx = NEWTON_ITERATION_CBRT(x, approx);
+  approx = NEWTON_ITERATION_CBRT(x, approx);
+  approx = NEWTON_ITERATION_CBRT(x, approx);
+  return NEWTON_ITERATION_CBRT(x, approx);
+}
+
+
 
 // ES6 draft 09-27-13, section 20.2.2.14.
 // Use Taylor series to approximate.
diff --git a/src/runtime.cc b/src/runtime.cc
index 2d760a4435..c49d24522d 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -7694,36 +7694,6 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_ConstructDouble) {
 }
 
 
-// Cube root approximation, refer to: http://metamerist.com/cbrt/cbrt.htm
-// Using initial approximation adapted from Kahan's cbrt and 4 iterations
-// of Newton's method.
-inline double CubeRootNewtonIteration(double approx, double x) {
-  return (1.0 / 3.0) * (x / (approx * approx) + 2 * approx);
-}
-
-
-inline double CubeRoot(double x) {
-  static const uint64_t magic = V8_2PART_UINT64_C(0x2A9F7893, 00000000);
-  uint64_t xhigh = double_to_uint64(x);
-  double approx = uint64_to_double(xhigh / 3 + magic);
-
-  approx = CubeRootNewtonIteration(approx, x);
-  approx = CubeRootNewtonIteration(approx, x);
-  approx = CubeRootNewtonIteration(approx, x);
-  return CubeRootNewtonIteration(approx, x);
-}
-
-
-RUNTIME_FUNCTION(MaybeObject*, Runtime_Math_cbrt) {
-  SealHandleScope shs(isolate);
-  ASSERT(args.length() == 1);
-  CONVERT_DOUBLE_ARG_CHECKED(x, 0);
-  if (x == 0 || std::isinf(x)) return args[0];
-  double result = (x > 0) ? CubeRoot(x) : -CubeRoot(-x);
-  return isolate->heap()->AllocateHeapNumber(result);
-}
-
-
 static const double kPiDividedBy4 = 0.78539816339744830962;
 
 
diff --git a/src/runtime.h b/src/runtime.h
index 480edaf239..d770968e20 100644
--- a/src/runtime.h
+++ b/src/runtime.h
@@ -175,7 +175,6 @@ namespace internal {
   F(Math_asin, 1, 1) \
   F(Math_atan, 1, 1) \
   F(Math_log, 1, 1) \
-  F(Math_cbrt, 1, 1) \
   F(Math_sqrt, 1, 1) \
   F(Math_exp, 1, 1) \
   F(Math_floor, 1, 1) \