diff --git a/CHANGELOG.md b/CHANGELOG.md
index cb748e37..b2e4244c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@ All notable changes to this project will be documented in this file.
 - `Obs` objects now have methods `is_zero` and `is_zero_within_error`
 
 ### Changed
+- Additional attributes can no longer be added to existing Obs. This makes it no longer possible to import Obs created with previous versions of pyerrors
 - The default value for Corr.prange is now `None`
 - The `input` module was restructured to contain one submodule per data source
 
diff --git a/pyerrors/pyerrors.py b/pyerrors/pyerrors.py
index 55e40d48..fa30c0f4 100644
--- a/pyerrors/pyerrors.py
+++ b/pyerrors/pyerrors.py
@@ -8,7 +8,6 @@ import autograd.numpy as anp  # Thinly-wrapped numpy
 from autograd import jacobian
 import matplotlib.pyplot as plt
 import numdifftools as nd
-import scipy.special
 
 
 class Obs: