diff --git a/model_server/base/roiset.py b/model_server/base/roiset.py
index e81847126e6ed78fa9808b8ae0af466ca760e3be..925b3b7b9ea0ae2056fb89d2c6df00b72f9797ab 100644
--- a/model_server/base/roiset.py
+++ b/model_server/base/roiset.py
@@ -1152,7 +1152,7 @@ class RoiSetWithDerivedChannels(RoiSet):
             self.get_patch_masks_acc(expanded=False, pad_to=None)
         )
 
-        self._df['classify_by_' + name] = pd.Series(dtype='Int64')
+        self._df['classify_by_' + name] = pd.Series(dtype='Int16')
 
         for i, roi in enumerate(self):
             oc = np.unique(