diff --git a/src/ert/storage/migration/to7.py b/src/ert/storage/migration/to7.py
index 0c81c7cd1dd..a7a0b6569d0 100644
--- a/src/ert/storage/migration/to7.py
+++ b/src/ert/storage/migration/to7.py
@@ -240,6 +240,15 @@ def _migrate_responses_from_netcdf_to_parquet(path: Path) -> None:
                                 polars.col("time").dt.cast_time_unit("ms")
                             )
 
+                        # Ensure "response_key" is the first column
+                        polars_df = polars_df.select(
+                            ["response_key"]
+                            + [
+                                col
+                                for col in polars_df.columns
+                                if col != "response_key"
+                            ]
+                        )
                         polars_df.write_parquet(real_dir / f"{ds_name}.parquet")
 
                         os.remove(real_dir / f"{ds_name}.nc")