diff --git a/dom/media/webaudio/AudioEventTimeline.cpp b/dom/media/webaudio/AudioEventTimeline.cpp
index 66cb362882ec..3723e304d7d1 100644
--- a/dom/media/webaudio/AudioEventTimeline.cpp
+++ b/dom/media/webaudio/AudioEventTimeline.cpp
@@ -37,11 +37,12 @@ static float ExtractValueFromCurve(double startTime, float* aCurve, uint32_t aCu
   if (ratio >= 1.0) {
     return aCurve[aCurveLength - 1];
   }
-  uint32_t current = uint32_t(aCurveLength * ratio);
+  uint32_t current = uint32_t(floor((aCurveLength - 1) * ratio));
   uint32_t next = current + 1;
+  double step = duration / double(aCurveLength - 1);
   if (next < aCurveLength) {
-    double t0 = double(current) / double(aCurveLength) * duration ;
-    double t1 = double(next) / double(aCurveLength) * duration ;
+    double t0 = current * step;
+    double t1 = next * step;
     return LinearInterpolate(t0, aCurve[current], t1, aCurve[next], t - startTime);
   } else {
     return aCurve[current];
diff --git a/dom/media/webaudio/compiledtest/TestAudioEventTimeline.cpp b/dom/media/webaudio/compiledtest/TestAudioEventTimeline.cpp
index 2f347f5f96c1..3c35dee29bb4 100644
--- a/dom/media/webaudio/compiledtest/TestAudioEventTimeline.cpp
+++ b/dom/media/webaudio/compiledtest/TestAudioEventTimeline.cpp
@@ -102,7 +102,11 @@ void TestSpecExample()
 
   ErrorResultMock rv;
 
-  float curve[] = { -1.0f, 0.0f, 1.0f };
+  uint32_t curveLength = 44100;
+  float* curve = new float[curveLength];
+  for (uint32_t i = 0; i < curveLength; ++i) {
+    curve[i] = sin(M_PI * i / float(curveLength));
+  }
 
   // This test is copied from the example in the Web Audio spec
   const double t0 = 0.0,
@@ -127,7 +131,7 @@ void TestSpecExample()
   is(rv, NS_OK, "ExponentialRampToValueAtTime succeeded");
   timeline.ExponentialRampToValueAtTime(0.05f, t6, rv);
   is(rv, NS_OK, "ExponentialRampToValueAtTime succeeded");
-  timeline.SetValueCurveAtTime(curve, ArrayLength(curve), t6, t7 - t6, rv);
+  timeline.SetValueCurveAtTime(curve, curveLength, t6, t7 - t6, rv);
   is(rv, NS_OK, "SetValueCurveAtTime succeeded");
 
   is(timeline.GetValueAtTime(0.0), 0.2f, "Correct value");
@@ -144,10 +148,11 @@ void TestSpecExample()
   is(timeline.GetValueAtTime(0.55), (0.15f * powf(0.75f / 0.15f, 0.15f / 0.2f)), "Correct value");
   is(timeline.GetValueAtTime(0.6), 0.75f, "Correct value");
   is(timeline.GetValueAtTime(0.65), (0.75f * powf(0.05f / 0.75f, 0.5f)), "Correct value");
-  is(timeline.GetValueAtTime(0.7), -1.0f, "Correct value");
-  is(timeline.GetValueAtTime(0.8), 0.0f, "Correct value");
-  is(timeline.GetValueAtTime(0.9), 1.0f, "Correct value");
-  is(timeline.GetValueAtTime(1.0), 1.0f, "Correct value");
+  is(timeline.GetValueAtTime(0.7), 0.0f, "Correct value");
+  is(timeline.GetValueAtTime(0.85), 1.0f, "Correct value");
+  is(timeline.GetValueAtTime(1.0), curve[curveLength - 1], "Correct value");
+
+  delete[] curve;
 }
 
 void TestInvalidEvents()
diff --git a/dom/media/webaudio/test/test_audioParamSetCurveAtTime.html b/dom/media/webaudio/test/test_audioParamSetCurveAtTime.html
index 81ccbcb421ba..bcb655b52d6f 100644
--- a/dom/media/webaudio/test/test_audioParamSetCurveAtTime.html
+++ b/dom/media/webaudio/test/test_audioParamSetCurveAtTime.html
@@ -30,13 +30,14 @@ var gTest = {
     this.curve = new Float32Array([1.0, 0.5, 0.75, 0.25]);
     var expectedBuffer = context.createBuffer(1, 2048, context.sampleRate);
     var data = expectedBuffer.getChannelData(0);
+    var step = 1024 / 3;
     for (var i = 0; i < 2048; ++i) {
-      if (i < 256) {
-        data[i] = 1.0 - 0.5*i/256;
-      } else if (i < 512) {
-        data[i] = 0.5 + 0.25*(i - 256)/256;
-      } else if (i < 768) {
-        data[i] = 0.75 - 0.5*(i - 512)/256;
+      if (i < step) {
+        data[i] = 1.0 - 0.5*i/step;
+      } else if (i < 2*step) {
+        data[i] = 0.5 + 0.25*(i - step)/step;
+      } else if (i < 3*step) {
+        data[i] = 0.75 - 0.5*(i - 2*step)/step;
       } else {
         data[i] = 0.25;
       }
diff --git a/dom/media/webaudio/test/test_audioParamSetCurveAtTimeTwice.html b/dom/media/webaudio/test/test_audioParamSetCurveAtTimeTwice.html
index 97afd17ae25d..0f976380e077 100644
--- a/dom/media/webaudio/test/test_audioParamSetCurveAtTimeTwice.html
+++ b/dom/media/webaudio/test/test_audioParamSetCurveAtTimeTwice.html
@@ -47,15 +47,13 @@ var gTest = {
     }
     var expectedBuffer = context.createBuffer(1, 2048, context.sampleRate);
     for (var i = 0; i < 2048; ++i) {
-      var t = i / context.sampleRate;
-      var current = Math.min(99, Math.floor(100 * Math.min(1.0, (t - T0) / this.duration)));
+      step = 1024.0/99.0;
+      var current = Math.floor(i / step);
       var next = current + 1;
       if (next < this.curve.length) {
-        var t0 = current / this.curve.length * this.duration;
-        var t1 = next / this.curve.length * this.duration;
-        expectedBuffer.getChannelData(0)[i] = linearInterpolate(t0, this.curve[current], t1, this.curve[next], t);
+        expectedBuffer.getChannelData(0)[i] = linearInterpolate(current*step, this.curve[current], next*step, this.curve[next], i);
       } else {
-        expectedBuffer.getChannelData(0)[i] = this.curve[current];
+        expectedBuffer.getChannelData(0)[i] = this.curve[99];
       }
     }
     return expectedBuffer;