diff --git a/src/ctapipe/io/interpolation.py b/src/ctapipe/io/interpolation.py
index b68adbf6bf4..5870e71a91b 100644
--- a/src/ctapipe/io/interpolation.py
+++ b/src/ctapipe/io/interpolation.py
@@ -11,6 +11,8 @@
 
 from .astropy_helpers import read_table
 
+dimensionless_unit = u.Unit()
+
 
 class StepFunction:
 
@@ -236,6 +238,8 @@ class FlatFieldInterpolator(Interpolator):
     """
 
     telescope_data_group = "dl1/calibration/gain"  # TBD
+    required_columns = frozenset(["time", "gain"])  # TBD
+    expected_units = {"gain": dimensionless_unit}
 
     def __call__(self, tel_id, time):
         """
@@ -273,8 +277,6 @@ def add_table(self, tel_id, input_table):
             for the flatfield data
         """
 
-        self.required_columns = frozenset(["time", "gain"])  # TBD
-
         self._check_tables(input_table)
 
         input_table.sort("time")
@@ -292,6 +294,8 @@ class PedestalInterpolator(Interpolator):
     """
 
     telescope_data_group = "dl1/calibration/pedestal"  # TBD
+    required_columns = frozenset(["time", "pedestal"])  # TBD
+    expected_units = {"pedestal": dimensionless_unit}
 
     def __call__(self, tel_id, time):
         """
@@ -329,8 +333,6 @@ def add_table(self, tel_id, input_table):
             for the pedestal data
         """
 
-        self.required_columns = frozenset(["time", "pedestal"])  # TBD
-
         self._check_tables(input_table)
 
         input_table.sort("time")
diff --git a/src/ctapipe/io/tests/test_interpolator.py b/src/ctapipe/io/tests/test_interpolator.py
index 4d41ceeff0b..930e1e7d73c 100644
--- a/src/ctapipe/io/tests/test_interpolator.py
+++ b/src/ctapipe/io/tests/test_interpolator.py
@@ -104,14 +104,16 @@ def test_bounds():
     table_pedestal = Table(
         {
             "time": np.arange(0.0, 10.1, 2.0),
-            "pedestal": np.reshape(np.random.normal(4.0, 1.0, 1850 * 6), (6, 1850)),
+            "pedestal": np.reshape(np.random.normal(4.0, 1.0, 1850 * 6), (6, 1850))
+            * u.Unit(),
         },
     )
 
     table_flatfield = Table(
         {
             "time": np.arange(0.0, 10.1, 2.0),
-            "gain": np.reshape(np.random.normal(1.0, 1.0, 1850 * 6), (6, 1850)),
+            "gain": np.reshape(np.random.normal(1.0, 1.0, 1850 * 6), (6, 1850))
+            * u.Unit(),
         },
     )