diff --git a/Formula.cs b/Formula.cs
index 0a5d8c2..023b260 100644
--- a/Formula.cs
+++ b/Formula.cs
@@ -2712,7 +2712,7 @@ public dynamic LexerPerformAction(int avoidingNameCollisions, string Yy_Start)
 break;
 case 29:return 18;
 break;
-case 30:return undefined;
+case 30:return "PI";
 break;
 case 31:return 23;
 break;