diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index db6cadd..af2f26d 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -18,8 +18,8 @@
 Deprecations:
 ^^^^^^^^^^^^^
 
-*none*
-
+- Deprecated ``OpenSSL.tsafe``.
+  `#673 <https://github.com/pyca/pyopenssl/pull/673>`_
 
 Changes:
 ^^^^^^^^
diff --git a/src/OpenSSL/tsafe.py b/src/OpenSSL/tsafe.py
index 1cc0d2b..f1c6f67 100644
--- a/src/OpenSSL/tsafe.py
+++ b/src/OpenSSL/tsafe.py
@@ -1,8 +1,15 @@
+import warnings
 from threading import RLock as _RLock
 
 from OpenSSL import SSL as _ssl
 
 
+warnings.warn(
+    "OpenSSL.tsafe is deprecated and will be removed",
+    DeprecationWarning, stacklevel=3
+)
+
+
 class Connection:
     def __init__(self, *args):
         self._ssl_conn = _ssl.Connection(*args)