diff --git a/dom/html/HTMLInputElement.cpp b/dom/html/HTMLInputElement.cpp
index c5849de49e..dd2d134f8e 100644
--- a/dom/html/HTMLInputElement.cpp
+++ b/dom/html/HTMLInputElement.cpp
@@ -3105,6 +3105,26 @@ HTMLInputElement::GetFiles()
   return mFileList;
 }
 
+void
+HTMLInputElement::SetFiles(FileList* aFiles)
+{
+  if (mType != NS_FORM_INPUT_FILE || !aFiles) {
+    return;
+  }
+
+  // Clear |mFileList| to omit |UpdateFileList|
+  if (mFileList) {
+    mFileList->Clear();
+    mFileList = nullptr;
+  }
+
+  // Update |mFilesOrDirectories|
+  SetFiles(aFiles, true);
+
+  // Update |mFileList| without copy
+  mFileList = aFiles;
+}
+
 /* static */ void
 HTMLInputElement::HandleNumberControlSpin(void* aData)
 {
diff --git a/dom/html/HTMLInputElement.h b/dom/html/HTMLInputElement.h
index 16651d5200..24fc7454ac 100644
--- a/dom/html/HTMLInputElement.h
+++ b/dom/html/HTMLInputElement.h
@@ -474,6 +474,7 @@ public:
   // XPCOM GetForm() is OK
 
   FileList* GetFiles();
+  void SetFiles(FileList* aFiles);
 
   // XPCOM GetFormAction() is OK
   void SetFormAction(const nsAString& aValue, ErrorResult& aRv)
diff --git a/dom/webidl/HTMLInputElement.webidl b/dom/webidl/HTMLInputElement.webidl
index 93ad90f456..528689bbd1 100644
--- a/dom/webidl/HTMLInputElement.webidl
+++ b/dom/webidl/HTMLInputElement.webidl
@@ -40,7 +40,7 @@ interface HTMLInputElement : HTMLElement {
            attribute boolean disabled;
   readonly attribute HTMLFormElement? form;
   [Pure]
-  readonly attribute FileList? files;
+           attribute FileList? files;
   [CEReactions, Pure, SetterThrows]
            attribute DOMString formAction;
   [CEReactions, Pure, SetterThrows]