diff --git a/src/finam/data/tools/core.py b/src/finam/data/tools/core.py
index fc397374604973d42287620a3ca5ffcb63496d2d..ecb7809e9f3a832d50a5ac0df9807db94467bfee 100644
--- a/src/finam/data/tools/core.py
+++ b/src/finam/data/tools/core.py
@@ -9,7 +9,6 @@ import pandas as pd
 from ...errors import FinamDataError
 from .. import grid_spec
 from ..grid_base import Grid
-from .mask import is_masked_array
 from .units import (
     UNITS,
     check_quantified,