diff --git a/src/protocol/ast_printer.rs b/src/protocol/ast_printer.rs
index 8a059052ecad78939c48f82b234610db38ebccbd..1075d78961a11fdf554c641ea1d37715f0fc50bb 100644
--- a/src/protocol/ast_printer.rs
+++ b/src/protocol/ast_printer.rs
@@ -541,9 +541,9 @@ impl ASTWriter {
                 let indent3 = indent2 + 1;
                 let indent4 = indent3 + 1;
                 for case in &stmt.cases {
-                    if let Some(guard_var_id) = case.guard_var {
+                    if !case.guard_var.is_invalid() {
                         self.kv(indent3).with_s_key("GuardStatement");
-                        self.write_stmt(heap, guard_var_id.upcast().upcast(), indent4);
+                        self.write_stmt(heap, case.guard_var.upcast().upcast(), indent4);
                     } else {
                         self.kv(indent3).with_s_key("GuardStatement").with_s_val("None");
                     }