diff --git a/quantities/quantity.py b/quantities/quantity.py
@@ -629,7 +629,7 @@ def nanargmin(self,axis=None, out=None):
    def nanargmax(self,axis=None, out=None):
        return np.nanargmax(self.magnitude)

-    @with_doc(np.ndarray.ptp)
    def ptp(self, axis=None, out=None):
        ret = np.ptp(self.magnitude, axis, None if out is None else out.magnitude)
        dim = self.dimensionality