diff --git a/parser/html/nsHtml5TreeOperation.h b/parser/html/nsHtml5TreeOperation.h
index 0b2970738e..a93f44c46f 100644
--- a/parser/html/nsHtml5TreeOperation.h
+++ b/parser/html/nsHtml5TreeOperation.h
@@ -108,7 +108,7 @@ class nsHtml5TreeOperation {
       }
       nsAutoString str;
       aAtom->ToString(str);
-      return NS_Atomize(str);
+      return NS_AtomizeMainThread(str);
     }
 
     static nsresult AppendTextToTextNode(const char16_t* aBuffer,