diff --git a/dom/html/HTMLSourceElement.cpp b/dom/html/HTMLSourceElement.cpp
index df8cf9dda8..afe481dfd7 100644
--- a/dom/html/HTMLSourceElement.cpp
+++ b/dom/html/HTMLSourceElement.cpp
@@ -133,6 +133,9 @@ HTMLSourceElement::AfterSetAttr(int32_t aNameSpaceID, nsIAtom* aName,
   } else if (aNameSpaceID == kNameSpaceID_None && aName == nsGkAtoms::media) {
     UpdateMediaList(aValue);
   } else if (aNameSpaceID == kNameSpaceID_None && aName == nsGkAtoms::src) {
+    mSrcTriggeringPrincipal = nsContentUtils::GetAttrTriggeringPrincipal(
+        this, aValue ? aValue->GetStringValue() : EmptyString(),
+        aMaybeScriptedPrincipal);
     mSrcMediaSource = nullptr;
     if (aValue) {
       nsString srcStr = aValue->GetStringValue();
diff --git a/dom/html/HTMLSourceElement.h b/dom/html/HTMLSourceElement.h
index 7312c91e33..aeaf884c81 100644
--- a/dom/html/HTMLSourceElement.h
+++ b/dom/html/HTMLSourceElement.h
@@ -56,13 +56,17 @@ public:
   MediaSource* GetSrcMediaSource() { return mSrcMediaSource; };
 
   // WebIDL
-  void GetSrc(nsString& aSrc)
+  void GetSrc(nsString& aSrc, nsIPrincipal&)
   {
     GetURIAttr(nsGkAtoms::src, nullptr, aSrc);
   }
-  void SetSrc(const nsAString& aSrc, mozilla::ErrorResult& rv)
+  void SetSrc(const nsAString& aSrc, nsIPrincipal& aTriggeringPrincipal, mozilla::ErrorResult& rv)
   {
-    SetHTMLAttr(nsGkAtoms::src, aSrc, rv);
+    SetHTMLAttr(nsGkAtoms::src, aSrc, aTriggeringPrincipal, rv);
+  }
+  nsIPrincipal* GetSrcTriggeringPrincipal() const
+  {
+    return mSrcTriggeringPrincipal;
   }
 
   void GetType(DOMString& aType)
@@ -117,6 +121,9 @@ private:
   RefPtr<nsMediaList> mMediaList;
   RefPtr<MediaSource> mSrcMediaSource;
 
+  // The triggering principal for the src attribute.
+  nsCOMPtr<nsIPrincipal> mSrcTriggeringPrincipal;
+
   // Generates a new nsMediaList using the given input
   void UpdateMediaList(const nsAttrValue* aValue);
 };
diff --git a/dom/webidl/HTMLSourceElement.webidl b/dom/webidl/HTMLSourceElement.webidl
index 55f25e469c..78570b8579 100644
--- a/dom/webidl/HTMLSourceElement.webidl
+++ b/dom/webidl/HTMLSourceElement.webidl
@@ -13,7 +13,7 @@
 
 [HTMLConstructor]
 interface HTMLSourceElement : HTMLElement {
-           [CEReactions, SetterThrows]
+           [CEReactions, NeedsSubjectPrincipal, SetterThrows]
            attribute DOMString src;
            [CEReactions, SetterThrows]
            attribute DOMString type;