diff --git a/mode/css.py b/mode/css.py
index 6406662..be261ec 100644
--- a/mode/css.py
+++ b/mode/css.py
@@ -30,8 +30,8 @@ class CSSGrammar(Grammar):
         NocasePatternRule(r'css.rule', r'@(?:page|media|import)'),
         NocasePatternRule(r'css.color', r'(?:aqua|black|blue|fuchsia|gray|green|lime|maroon|navy|olive|orange|purple|red|silver|teal|white|yellow|#\d{6}|#\d{3})(?!' + chr2 + ')'),
 
-        NocasePatternRule(r'css.keyword', r'(?:url|rgb|counter)'),
-        NocaseRegionRule(r'css.keyword', '(?:(?<=url)|(?<=rgb)|(?<=counter))\(', KeywordGrammar, '\)'),
+        NocasePatternRule(r'css.keyword', r'(?:url|rgba|rgb|counter)'),
+        NocaseRegionRule(r'css.keyword', '(?:(?<=url)|(?<=rgba)|(?<=rgb)|(?<=counter))\(', KeywordGrammar, '\)'),
 
         NocasePatternRule(r'css.label', r"\.?" + chr2 + "+(?= *{)"),
         NocasePatternRule(r'css.ident', r"-?[a-z_]" + chr2 + "*"),