diff --git a/trollimage/xrimage.py b/trollimage/xrimage.py
index da0b28f8..be218c03 100644
--- a/trollimage/xrimage.py
+++ b/trollimage/xrimage.py
@@ -1097,7 +1097,7 @@ def _check_stretch_value(self, val, kind='min'):
             val = self.xrify_tuples(val)
 
         dtype = self.data.dtype
-        if isinstance(dtype, (np.uint8, np.int8, np.uint16, np.int16)):
+        if dtype in (np.uint8, np.int8, np.uint16, np.int16):
             dtype = np.dtype(np.float32)
         elif np.issubdtype(dtype, np.integer) or isinstance(dtype, int):
             dtype = np.dtype(np.float64)