diff --git a/bcolz/ctable.py b/bcolz/ctable.py
index 459ff578..e6cf01f2 100644
--- a/bcolz/ctable.py
+++ b/bcolz/ctable.py
@@ -139,6 +139,7 @@ def cparams(self):
         "The compression parameters for this object."
         return self._cparams
 
+    self._dtype = None
     @property
     def dtype(self):
         "The data type of this object (numpy dtype)."
@@ -226,8 +227,6 @@ def __init__(self, columns=None, names=None, **kwargs):
         # Attach the attrs to this object
         self.attrs = attrs.attrs(self.rootdir, self.mode, _new=_new)
 
-        # Trigger update of dtype cache
-        self._dtype = None
         # Cache a structured array of len 1 for ctable[int] acceleration
         self._arr1 = np.empty(shape=(1,), dtype=self.dtype)