diff --git a/cql2/standard/schema/cql2.bnf b/cql2/standard/schema/cql2.bnf
index cbdb7294..658a8281 100644
--- a/cql2/standard/schema/cql2.bnf
+++ b/cql2/standard/schema/cql2.bnf
@@ -352,7 +352,7 @@ identifierStart = "\x003A"              # colon
 #=============================================================================#
 # Definition of a FUNCTION
 #=============================================================================#
-function = identifier "(" {argumentList} ")";
+function = identifier "(" [argumentList] ")";
 
 argumentList = argument [ { "," argument } ];