diff --git a/dom/media/webaudio/AudioBufferSourceNode.cpp b/dom/media/webaudio/AudioBufferSourceNode.cpp
index 7a1d9cc80f59..e09dc079264e 100644
--- a/dom/media/webaudio/AudioBufferSourceNode.cpp
+++ b/dom/media/webaudio/AudioBufferSourceNode.cpp
@@ -702,9 +702,9 @@ void
 AudioBufferSourceNode::Start(double aWhen, double aOffset,
                              const Optional<double>& aDuration, ErrorResult& aRv)
 {
-  if (!WebAudioUtils::IsTimeValid(aWhen) ||
+  if (!WebAudioUtils::IsTimeValid(aWhen) || aOffset < 0 ||
       (aDuration.WasPassed() && !WebAudioUtils::IsTimeValid(aDuration.Value()))) {
-    aRv.Throw(NS_ERROR_DOM_NOT_SUPPORTED_ERR);
+    aRv.Throw(NS_ERROR_RANGE_ERR);
     return;
   }
 
@@ -805,7 +805,7 @@ void
 AudioBufferSourceNode::Stop(double aWhen, ErrorResult& aRv)
 {
   if (!WebAudioUtils::IsTimeValid(aWhen)) {
-    aRv.Throw(NS_ERROR_DOM_NOT_SUPPORTED_ERR);
+    aRv.Throw(NS_ERROR_RANGE_ERR);
     return;
   }