diff --git a/dpdata/plugins/ase.py b/dpdata/plugins/ase.py
index 33f1c5ee..01c8483b 100644
--- a/dpdata/plugins/ase.py
+++ b/dpdata/plugins/ase.py
@@ -11,6 +11,7 @@
 if TYPE_CHECKING:
     import ase
     from ase.optimize.optimize import Optimizer
+    from ase.io import Trajectory
 
 
 @Format.register("ase/structure")