diff --git a/js/src/tests/ecma_6/TypedObject/simd/float32x4clamp.js b/js/src/tests/ecma_6/TypedObject/simd/float32x4clamp.js
index 4f5775f28244..a27d62503de7 100644
--- a/js/src/tests/ecma_6/TypedObject/simd/float32x4clamp.js
+++ b/js/src/tests/ecma_6/TypedObject/simd/float32x4clamp.js
@@ -3,20 +3,19 @@ var BUGNUMBER = 946042;
 var float32x4 = SIMD.float32x4;
 var int32x4 = SIMD.int32x4;
 
-var summary = 'float32x4 add';
+var summary = 'float32x4 clamp';
 
 function test() {
   print(BUGNUMBER + ": " + summary);
 
-  // FIXME -- Bug 948379: Amend to check for correctness of border cases.
-
-  var a = float32x4(1, 2, 3, 4);
-  var b = float32x4(10, 20, 30, 40);
-  var c = SIMD.float32x4.add(a, b);
-  assertEq(c.x, 11);
-  assertEq(c.y, 22);
-  assertEq(c.z, 33);
-  assertEq(c.w, 44);
+  var a = float32x4(-13.37, 10.46, 31.79, 0.54);
+  var lower = float32x4(2.1, 1.1, 50.13, 0.0);
+  var upper = float32x4(2.56, 5.55, 55.93, 1.1);
+  var c = SIMD.float32x4.clamp(a, lower, upper);
+  assertEq(c.x, Math.fround(2.1));
+  assertEq(c.y, Math.fround(5.55));
+  assertEq(c.z, Math.fround(50.13));
+  assertEq(c.w, Math.fround(0.54));
 
   if (typeof reportCompare === "function")
     reportCompare(true, true);