diff --git a/crates/s3/src/select.rs b/crates/s3/src/select.rs
index a752244..15f6d2a 100644
--- a/crates/s3/src/select.rs
+++ b/crates/s3/src/select.rs
@@ -246,12 +246,24 @@ mod tests {
         assert!(matches!(e, Error::General(_)));
     }
 
+    #[test]
+    fn classify_unknown_code_with_not_implemented_text_maps_unsupported_feature() {
+        let e = classify_aws_code(Some("SlowDown"), "backend replied with NotImplemented");
+        assert!(matches!(e, Error::UnsupportedFeature(msg) if msg.contains("does not support")));
+    }
+
     #[test]
     fn classify_missing_code_unknown_maps_general() {
         let e = classify_aws_code(None, "Service error: query parsing failed");
         assert!(matches!(e, Error::General(_)));
     }
 
+    #[test]
+    fn classify_missing_code_maps_not_implemented_substring() {
+        let e = classify_aws_code(None, "Service error: backend returned NotImplemented");
+        assert!(matches!(e, Error::UnsupportedFeature(msg) if msg.contains("does not support")));
+    }
+
     #[test]
     fn parquet_rejects_whole_object_compression() {
         let options = SelectOptions {