diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7fb327a..2f7ca62 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,11 @@ All notable changes in pdfminer.six will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
+## [Unreleased]
+
+### Removed
+- Unused dependency on `sortedcontainers` package ([#525](https://github.com/pdfminer/pdfminer.six/pull/525))
+
 ## [20201018]
 
 ### Deprecated
diff --git a/setup.py b/setup.py
index 1a96ab4..bb07b40 100644
--- a/setup.py
+++ b/setup.py
@@ -15,7 +15,6 @@ setup(
     install_requires=[
         'chardet ; python_version > "3.0"',
         'cryptography',
-        'sortedcontainers',
     ],
     extras_require={
         "dev": ["nose", "tox"],