diff --git a/components/style/binding_tools/regen_atoms.py b/components/style/binding_tools/regen_atoms.py
index b14a30dd0e0..0950c0d7212 100755
--- a/components/style/binding_tools/regen_atoms.py
+++ b/components/style/binding_tools/regen_atoms.py
@@ -51,7 +51,7 @@ class CSSPseudoElementsAtomSource:
 
 
 class CSSAnonBoxesAtomSource:
-    PATTERN = re.compile('^(?:CSS_ANON_BOX|CSS_NON_INHERITING_ANON_BOX)\((.+),\s*"(.*)"\)')
+    PATTERN = re.compile('^(?:CSS_ANON_BOX|CSS_NON_INHERITING_ANON_BOX)\((.+),\s*"(.*)"(\,|\))')
     FILE = "include/nsCSSAnonBoxList.h"
     CLASS = "nsCSSAnonBoxes"
     TYPE = "nsICSSAnonBoxPseudo"