diff --git a/climetlab/loaders/__init__.py b/climetlab/loaders/__init__.py
index 65ce481c..a401fec1 100644
--- a/climetlab/loaders/__init__.py
+++ b/climetlab/loaders/__init__.py
@@ -257,7 +257,8 @@ class FastWriter(ArrayLike):
     def __init__(self, array, shape):
         self.array = array
         self.shape = shape
-        self.cache = np.zeros(shape)
+        self.dtype = array.dtype
+        self.cache = np.zeros(shape, dtype=self.dtype)
 
     def __setitem__(self, key, value):
         self.cache[key] = value
@@ -323,6 +324,7 @@ class OffsetView(ArrayLike):
 
     def __init__(self, large_array, *, offset, axis, shape):
         self.large_array = large_array
+        self.dtype = large_array.dtype
         self.offset = offset
         self.axis = axis
         self.shape = shape
diff --git a/climetlab/utils/config.py b/climetlab/utils/config.py
index 127568ff..9461535c 100644
--- a/climetlab/utils/config.py
+++ b/climetlab/utils/config.py
@@ -1191,18 +1191,16 @@ def parse_config(self):
         assert isinstance(self.end, datetime.date), (type(self.end), self.end)
         self.step = datetime.timedelta(days=self.step)
 
-        if isinstance(self.group_by, int) and self.group_by > 1:
+        if isinstance(self.group_by, int) and self.group_by > 0:
             self.grouper_key = GroupByDays(self.group_by)
         else:
             self.grouper_key = {
-                1: lambda dt: 0,  # only one group
+                0: lambda dt: 0,  # only one group
                 "monthly": lambda dt: (dt.year, dt.month),
                 "daily": lambda dt: (dt.year, dt.month, dt.day),
                 "MMDD": lambda dt: (dt.month, dt.day),
             }[self.group_by]
 
-        # assert False, self.grouper_key
-
     def format(self, x):
         return x.isoformat()
 
diff --git a/climetlab/version b/climetlab/version
index f9b0c0dc..3f2bb467 100644
--- a/climetlab/version
+++ b/climetlab/version
@@ -1 +1 @@
-0.18.14
+0.18.15