diff --git a/dom/media/TextTrackRegion.cpp b/dom/media/TextTrackRegion.cpp
index 9a82011cd125..0ddfb20d1542 100644
--- a/dom/media/TextTrackRegion.cpp
+++ b/dom/media/TextTrackRegion.cpp
@@ -5,7 +5,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "mozilla/dom/TextTrackRegion.h"
-#include "mozilla/dom/VTTRegionBinding.h"
 
 namespace mozilla {
 namespace dom {
@@ -45,6 +44,7 @@ TextTrackRegion::TextTrackRegion(nsISupports* aGlobal)
   , mRegionAnchorY(100)
   , mViewportAnchorX(0)
   , mViewportAnchorY(100)
+  , mScroll(ScrollSetting::_empty)
 {
 }
 
diff --git a/dom/media/TextTrackRegion.h b/dom/media/TextTrackRegion.h
index 892d7c7ad19d..cef0f7942506 100644
--- a/dom/media/TextTrackRegion.h
+++ b/dom/media/TextTrackRegion.h
@@ -12,6 +12,7 @@
 #include "nsWrapperCache.h"
 #include "mozilla/ErrorResult.h"
 #include "mozilla/dom/TextTrack.h"
+#include "mozilla/dom/VTTRegionBinding.h"
 #include "mozilla/Preferences.h"
 
 namespace mozilla {
@@ -116,19 +117,16 @@ class TextTrackRegion final : public nsISupports,
     }
   }
 
-  void GetScroll(nsAString& aScroll) const
+  ScrollSetting Scroll() const
   {
-    aScroll = mScroll;
+    return mScroll;
   }
 
-  void SetScroll(const nsAString& aScroll, ErrorResult& aRv)
+  void SetScroll(const ScrollSetting& aScroll)
   {
-    if (!aScroll.EqualsLiteral("") && !aScroll.EqualsLiteral("up")) {
-      aRv.Throw(NS_ERROR_DOM_SYNTAX_ERR);
-      return;
+    if (aScroll == ScrollSetting::_empty || aScroll == ScrollSetting::Up) {
+      mScroll = aScroll;
     }
-
-    mScroll = aScroll;
   }
 
   void GetId(nsAString& aId) const
@@ -149,10 +147,6 @@ class TextTrackRegion final : public nsISupports,
   void CopyValues(TextTrackRegion& aRegion);
 
   // -----helpers-------
-  const nsAString& Scroll() const
-  {
-    return mScroll;
-  }
   const nsAString& Id() const
   {
     return mId;
@@ -169,7 +163,7 @@ class TextTrackRegion final : public nsISupports,
   double mRegionAnchorY;
   double mViewportAnchorX;
   double mViewportAnchorY;
-  nsString mScroll;
+  ScrollSetting mScroll;
 
   // Helper to ensure new value is in the range: 0.0% - 100.0%; throws
   // an IndexSizeError otherwise.
diff --git a/dom/webidl/VTTRegion.webidl b/dom/webidl/VTTRegion.webidl
index df35eb2815db..d665cfea4c83 100644
--- a/dom/webidl/VTTRegion.webidl
+++ b/dom/webidl/VTTRegion.webidl
@@ -4,9 +4,14 @@
  * You can obtain one at http://mozilla.org/MPL/2.0/.
  *
  * The origin of this IDL file is
- *  http://dev.w3.org/html5/webvtt/#extension-of-the-texttrack-interface-for-region-support
+ * https://w3c.github.io/webvtt/#the-vttregion-interface
  */
 
+enum ScrollSetting {
+  "",
+  "up"
+};
+
 [Constructor, Pref="media.webvtt.regions.enabled"]
 interface VTTRegion {
            attribute DOMString id;
@@ -22,6 +27,6 @@ interface VTTRegion {
            attribute double viewportAnchorX;
            [SetterThrows]
            attribute double viewportAnchorY;
-           [SetterThrows]
-           attribute DOMString scroll;
+
+           attribute ScrollSetting scroll;
 };