diff --git a/ast-generator/src/build_fn/polymorphic_enum_loop_build_fn.rs b/ast-generator/src/build_fn/polymorphic_enum_loop_build_fn.rs
index 837df34..bcde9d4 100644
--- a/ast-generator/src/build_fn/polymorphic_enum_loop_build_fn.rs
+++ b/ast-generator/src/build_fn/polymorphic_enum_loop_build_fn.rs
@@ -86,7 +86,7 @@ pub fn make_polymorphic_enum_loop_build_fn(spec: &PolymorphicEnumLoopBuildSpec)
     } else {
         quote! { #pair_ident.into_inner() }
     };
-    
+
     let match_arms = spec
         .rules()
         .map(|rule| make_match_arm(spec, rule))
@@ -98,7 +98,7 @@ pub fn make_polymorphic_enum_loop_build_fn(spec: &PolymorphicEnumLoopBuildSpec)
             for inner_pair in #iter_expr {
                 match inner_pair.as_rule() {
                     #(#match_arms,)*
-                    _ => unreachable!()
+                    _ => unreachable!("Unexpected parse rule: {:?} (inner pair: {:#?}", inner_pair.as_rule(), inner_pair),
                 }
             }
             result.unwrap()
diff --git a/src/parser/ast.yaml b/src/parser/ast.yaml
index de46d99..ae1b2e9 100644
--- a/src/parser/ast.yaml
+++ b/src/parser/ast.yaml
@@ -919,6 +919,7 @@ AdditiveExpression:
       - MultiplicativeExpression:
           pass_through:
             kind: Expression
+            with: MultiplicativeExpression
       - AdditiveRhs:
           build:
             variant: Additive
@@ -954,6 +955,7 @@ MultiplicativeExpression:
       - PrefixExpression:
           pass_through:
             kind: Expression
+            with: PrefixExpression
       - MultiplicativeRhs:
           build:
             variant: Multiplicative