diff --git a/core/src/main/codegen/PolyAlgParser.jj b/core/src/main/codegen/PolyAlgParser.jj
index 3fbdb21340..dd4ce88d74 100644
--- a/core/src/main/codegen/PolyAlgParser.jj
+++ b/core/src/main/codegen/PolyAlgParser.jj
@@ -141,13 +141,13 @@ void OuterExpression() :
         <LCURL> InnerExpression() <RCURL>
         |
         Literal()
-    ) [OuterExpression()]  // outer expressions cannot contain separators, as they could not always be differentiated from a ListArgument
+    )+  // outer expressions cannot contain separators, as they could not always be differentiated from a ListArgument
 }
 
 void InnerExpression() : // An expression which appears within parentheses
 {}
 {
-    (
+    ((
         <LPAR> InnerExpression() <RPAR>
         |
         <LCURL> InnerExpression() <RCURL>
@@ -155,7 +155,7 @@ void InnerExpression() : // An expression which appears within parentheses
         Literal()
         |
         <AS>  // inner expressions can contain <AS>, since we know it cannot be an alias for an argument
-    ) (<SEP>)* [InnerExpression()]  // inner expressions can contain separators!
+    ) (<SEP>)* )*  // inner expressions can contain separators!
 }
 
 void Literal() :