diff --git a/js/src/builtin/SIMD.cpp b/js/src/builtin/SIMD.cpp
index e0dbba38d85..2ff61409f67 100644
--- a/js/src/builtin/SIMD.cpp
+++ b/js/src/builtin/SIMD.cpp
@@ -508,7 +508,7 @@ struct RecApprox {
 };
 template<typename T>
 struct RecSqrtApprox {
-    static inline T apply(T x) { return sqrt(1 / x); }
+    static inline T apply(T x) { return 1 / sqrt(x); }
 };
 template<typename T>
 struct Sqrt {
diff --git a/js/src/tests/ecma_7/SIMD/float32x4reciprocalsqrt.js b/js/src/tests/ecma_7/SIMD/float32x4reciprocalsqrt.js
index 10c29a8c8a6..cf1f5e13c51 100644
--- a/js/src/tests/ecma_7/SIMD/float32x4reciprocalsqrt.js
+++ b/js/src/tests/ecma_7/SIMD/float32x4reciprocalsqrt.js
@@ -6,7 +6,7 @@ var int32x4 = SIMD.int32x4;
 var summary = 'float32x4 reciprocalSqrt';
 
 function reciprocalsqrtf(a) {
-    return Math.fround(Math.sqrt(1 / Math.fround(a)));
+    return Math.fround(1 / Math.sqrt(a));
 }
 
 function test() {
diff --git a/js/src/tests/ecma_7/SIMD/float64x2-arithmetic.js b/js/src/tests/ecma_7/SIMD/float64x2-arithmetic.js
index 0f7b6564bb6..d23f5cff909 100644
--- a/js/src/tests/ecma_7/SIMD/float64x2-arithmetic.js
+++ b/js/src/tests/ecma_7/SIMD/float64x2-arithmetic.js
@@ -15,7 +15,7 @@ function mul(a, b) { return a * b; }
 function div(a, b) { return a / b; }
 function neg(a) { return -a; }
 function reciprocalApproximation(a) { return 1 / a; }
-function reciprocalSqrtApproximation(a) { return Math.sqrt(1 / a); }
+function reciprocalSqrtApproximation(a) { return 1 / Math.sqrt(a); }
 
 function testAdd(v, w) {
     return testBinaryFunc(v, w, float64x2.add, add);