diff --git a/src/test/pnf.rs b/src/test/pnf.rs
index 2303b3e..00daa3a 100644
--- a/src/test/pnf.rs
+++ b/src/test/pnf.rs
@@ -29,6 +29,11 @@ fn test_param_normalize() {
         dict.parse("<Seq <Digit 10>>~<Seq Char>").expect("parse errror").param_normalize(),
     );
 
+    assert_eq!(
+        dict.parse("<A~Y B>").expect("parse error"),
+        dict.parse("<A B>~<Y B>").expect("parse error").param_normalize(),
+    );
+
     assert_eq!(
         dict.parse("<A <B C~D~E> F~G H H>").expect("parse error"),
         dict.parse("<A <B C> F H H>