diff --git a/lavis/processors/randaugment.py b/lavis/processors/randaugment.py
index 5c6a9e6d6..736d5373b 100644
--- a/lavis/processors/randaugment.py
+++ b/lavis/processors/randaugment.py
@@ -23,6 +23,7 @@ def autocontrast_func(img, cutoff=0):
     n_bins = 256
 
     def tune_channel(ch):
+        ch = ch.astype(np.int16)
         n = ch.size
         cut = cutoff * n // 100
         if cut == 0: