diff --git a/dom/base/nsDocument.cpp b/dom/base/nsDocument.cpp
index 602da421a4..99f922c98b 100644
--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -5399,6 +5399,10 @@ nsDocument::CreateElement(const nsAString& aTagName,
   RefPtr<Element> elem = CreateElem(
     needsLowercase ? lcTagName : aTagName, nullptr, mDefaultElementType, is);
 
+  if (is) {
+    elem->SetAttr(kNameSpaceID_None, nsGkAtoms::is, *is, true);
+  }
+
   return elem.forget();
 }
 
@@ -5443,6 +5447,10 @@ nsDocument::CreateElementNS(const nsAString& aNamespaceURI,
     return nullptr;
   }
 
+  if (is) {
+    element->SetAttr(kNameSpaceID_None, nsGkAtoms::is, *is, true);
+  }
+
   return element.forget();
 }