diff --git a/crates/s3/src/select.rs b/crates/s3/src/select.rs
index a752244..8d34352 100644
--- a/crates/s3/src/select.rs
+++ b/crates/s3/src/select.rs
@@ -240,6 +240,12 @@ mod tests {
         assert!(matches!(e, Error::Auth(msg) if msg.contains("Access denied")));
     }
 
+    #[test]
+    fn classify_empty_code_maps_access_denied_substring() {
+        let e = classify_aws_code(Some(""), "Service error: ... AccessDenied ...");
+        assert!(matches!(e, Error::Auth(msg) if msg.contains("Access denied")));
+    }
+
     #[test]
     fn classify_maps_invalid_argument() {
         let e = classify_aws_code(Some("InvalidArgument"), "bad expr");