diff --git a/dom/base/nsContentUtils.cpp b/dom/base/nsContentUtils.cpp
index 792633de9139..67d23dc32106 100644
--- a/dom/base/nsContentUtils.cpp
+++ b/dom/base/nsContentUtils.cpp
@@ -9419,11 +9419,8 @@ void nsContentUtils::AppendDocumentLevelNativeAnonymousContentTo(
           "scroll frame should always implement nsIAnonymousContentCreator");
       creator->AppendAnonymousContentTo(aElements, 0);
     }
-
     if (nsCanvasFrame* canvasFrame = presShell->GetCanvasFrame()) {
-      if (Element* container = canvasFrame->GetCustomContentContainer()) {
-        aElements.AppendElement(container);
-      }
+      canvasFrame->AppendAnonymousContentTo(aElements, 0);
     }
   }
 
diff --git a/layout/generic/nsCanvasFrame.cpp b/layout/generic/nsCanvasFrame.cpp
index e1d260f54707..d07eb06e1a44 100644
--- a/layout/generic/nsCanvasFrame.cpp
+++ b/layout/generic/nsCanvasFrame.cpp
@@ -159,6 +159,9 @@ nsresult nsCanvasFrame::CreateAnonymousContent(
                                    nodeInfo.forget(), dom::NOT_FROM_PARSER);
     NS_ENSURE_SUCCESS(rv, rv);
 
+    mPopupgroupContent->SetProperty(nsGkAtoms::docLevelNativeAnonymousContent,
+                                    reinterpret_cast<void*>(true));
+
     aElements.AppendElement(mPopupgroupContent);
 
     nodeInfo = nodeInfoManager->GetNodeInfo(
@@ -175,9 +178,21 @@ nsresult nsCanvasFrame::CreateAnonymousContent(
     mTooltipContent->SetAttr(kNameSpaceID_None, nsGkAtoms::page,
                              NS_LITERAL_STRING("true"), false);
 
+    mTooltipContent->SetProperty(nsGkAtoms::docLevelNativeAnonymousContent,
+                                 reinterpret_cast<void*>(true));
+
     aElements.AppendElement(mTooltipContent);
   }
 
+#ifdef DEBUG
+  for (auto& element : aElements) {
+    MOZ_ASSERT(element.mContent->GetProperty(
+                   nsGkAtoms::docLevelNativeAnonymousContent),
+               "NAC from the canvas frame needs to be document-level, otherwise"
+               " it (1) inherits from the document which is unexpected, and (2)"
+               " StyleChildrenIterator won't be able to find it properly");
+  }
+#endif
   return NS_OK;
 }