diff --git a/crates/core/tests/lifecycle_import_dialect.rs b/crates/core/tests/lifecycle_import_dialect.rs
index 9ea2a3a..e229403 100644
--- a/crates/core/tests/lifecycle_import_dialect.rs
+++ b/crates/core/tests/lifecycle_import_dialect.rs
@@ -84,6 +84,18 @@ fn s3_filter_and_combination_is_flattened() {
     assert_eq!(config.rules[0].object_size_less_than, Some(1000));
 }
 
+#[test]
+fn s3_filter_and_rejects_duplicate_tag_keys() {
+    let error = parse_error(
+        r#"{"rules":[{"id":"r","status":"Enabled","filter":{"And":{"Tag":{"Key":"env","Value":"prod"},"Tags":[{"Key":"env","Value":"staging"}]}}}]}"#,
+    );
+
+    assert!(
+        error.contains("duplicate tag key in Filter.And: env"),
+        "{error}"
+    );
+}
+
 #[test]
 fn s3_standalone_object_size_greater_than_filter_is_accepted() {
     let config = parse(