diff --git a/src/motile_tracker/import_export/menus/import_dialog.py b/src/motile_tracker/import_export/menus/import_dialog.py
index 7a335812..14b05602 100644
--- a/src/motile_tracker/import_export/menus/import_dialog.py
+++ b/src/motile_tracker/import_export/menus/import_dialog.py
@@ -329,6 +329,65 @@ def _ensure_area_enabled(self) -> None:
             recompute = "area" not in self.tracks.graph.node_attr_keys()
             self.tracks.enable_features(["area"], recompute=recompute)
 
+    def _maybe_convert_legacy_masks(self, geff_dir: Path) -> Path | None:
+        """Offer to convert masks stored in an older, memory-heavy dtype.
+
+        Geff files written by older versions of tracksdata store segmentation
+        masks as integers (e.g. ``uint64``) rather than ``bool``, using ~8x more
+        memory when read. If such masks are detected, warn the user and offer a
+        lossless conversion. To keep the original (possibly shared) file
+        untouched, the conversion is written to a ``*_bool.geff`` copy next to
+        it, and that copy is loaded instead.
+
+        Returns:
+            Path | None: the geff directory to import (the original, or the
+            converted copy), or None if the user cancelled.
+        """
+        try:
+            from tracksdata.io import convert_geff_mask_to_bool, geff_mask_dtype
+        except ImportError:
+            return geff_dir  # older tracksdata without the utility; import as before
+
+        try:
+            dtype = geff_mask_dtype(geff_dir)
+        except Exception:  # noqa: BLE001
+            return geff_dir  # detection failed; don't block the import
+
+        if dtype is None or dtype == "bool":
+            return geff_dir
+
+        answer = QMessageBox.question(
+            self,
+            "Old mask format detected",
+            f"This geff stores segmentation masks as '{dtype}', an older format that "
+            "uses about 8x more memory when loaded.\n\n"
+            "Convert them to boolean now? A converted copy will be written next to the "
+            "original, which is left untouched.",
+            QMessageBox.Yes | QMessageBox.No | QMessageBox.Cancel,
+            QMessageBox.Yes,
+        )
+        if answer == QMessageBox.Cancel:
+            return None
+        if answer == QMessageBox.No:
+            return geff_dir  # load the original as-is
+
+        name = geff_dir.name
+        out_name = (
+            f"{name[:-5]}_bool.geff" if name.endswith(".geff") else f"{name}_bool"
+        )
+        out_path = geff_dir.parent / out_name
+
+        QApplication.setOverrideCursor(Qt.WaitCursor)
+        try:
+            if not out_path.exists():
+                convert_geff_mask_to_bool(geff_dir, output_path=out_path)
+        except Exception as e:  # noqa: BLE001
+            QMessageBox.critical(self, "Error", f"Failed to convert masks: {e}")
+            return None
+        finally:
+            QApplication.restoreOverrideCursor()
+        return out_path
+
     def _finish(self) -> None:
         """Tries to read the csv/geff file and optional segmentation image and apply the
         attribute to column mapping to construct a Tracks object"""
@@ -339,6 +398,10 @@ def _finish(self) -> None:
                 group_path = Path(self.import_widget.root.path)  # e.g. 'tracks'
                 geff_dir = store_path / group_path
 
+                geff_dir = self._maybe_convert_legacy_masks(geff_dir)
+                if geff_dir is None:
+                    return
+
                 self.name = self.import_widget.dir_name
                 scale = self.scale_widget.get_scale() if self.seg else None