diff --git a/dom/base/PostMessageEvent.cpp b/dom/base/PostMessageEvent.cpp
index ea89a43a18..2092e82977 100644
--- a/dom/base/PostMessageEvent.cpp
+++ b/dom/base/PostMessageEvent.cpp
@@ -32,16 +32,14 @@ PostMessageEvent::PostMessageEvent(nsGlobalWindow* aSource,
                                    const nsAString& aCallerOrigin,
                                    nsGlobalWindow* aTargetWindow,
                                    nsIPrincipal* aProvidedPrincipal,
-                                   nsIDocument* aSourceDocument,
-                                   bool aTrustedCaller)
-: StructuredCloneHolder(CloningSupported, TransferringSupported,
-                        StructuredCloneScope::SameProcessSameThread),
-  mSource(aSource),
-  mCallerOrigin(aCallerOrigin),
-  mTargetWindow(aTargetWindow),
-  mProvidedPrincipal(aProvidedPrincipal),
-  mSourceDocument(aSourceDocument),
-  mTrustedCaller(aTrustedCaller)
+                                   nsIDocument* aSourceDocument)
+  : StructuredCloneHolder(CloningSupported, TransferringSupported,
+                          StructuredCloneScope::SameProcessSameThread)
+  , mSource(aSource)
+  , mCallerOrigin(aCallerOrigin)
+  , mTargetWindow(aTargetWindow)
+  , mProvidedPrincipal(aProvidedPrincipal)
+  , mSourceDocument(aSourceDocument)
 {
   MOZ_COUNT_CTOR(PostMessageEvent);
 }
@@ -169,7 +167,7 @@ PostMessageEvent::Run()
   if (shell)
     presContext = shell->GetPresContext();
 
-  event->SetTrusted(mTrustedCaller);
+  event->SetTrusted(true);
   WidgetEvent* internalEvent = event->WidgetEventPtr();
 
   nsEventStatus status = nsEventStatus_eIgnore;
diff --git a/dom/base/PostMessageEvent.h b/dom/base/PostMessageEvent.h
index d96ac11403..a38e349c17 100644
--- a/dom/base/PostMessageEvent.h
+++ b/dom/base/PostMessageEvent.h
@@ -33,8 +33,7 @@ public:
                    const nsAString& aCallerOrigin,
                    nsGlobalWindow* aTargetWindow,
                    nsIPrincipal* aProvidedPrincipal,
-                   nsIDocument* aSourceDocument,
-                   bool aTrustedCaller);
+                   nsIDocument* aSourceDocument);
 
 private:
   ~PostMessageEvent();
@@ -44,7 +43,6 @@ private:
   RefPtr<nsGlobalWindow> mTargetWindow;
   nsCOMPtr<nsIPrincipal> mProvidedPrincipal;
   nsCOMPtr<nsIDocument> mSourceDocument;
-  bool mTrustedCaller;
 };
 
 } // namespace dom
diff --git a/dom/base/nsGlobalWindow.cpp b/dom/base/nsGlobalWindow.cpp
index 3ef2f6cd8c..7e58b273f0 100644
--- a/dom/base/nsGlobalWindow.cpp
+++ b/dom/base/nsGlobalWindow.cpp
@@ -8885,8 +8885,7 @@ nsGlobalWindow::PostMessageMozOuter(JSContext* aCx, JS::Handle<JS::Value> aMessa
                          providedPrincipal,
                          callerInnerWin
                          ? callerInnerWin->GetDoc()
-                         : nullptr,
-                         nsContentUtils::IsCallerChrome());
+                         : nullptr);
 
   JS::Rooted<JS::Value> message(aCx, aMessage);
   JS::Rooted<JS::Value> transfer(aCx, aTransfer);