diff --git a/CHANGES b/CHANGES
index 5db63af87..758ab061c 100644
--- a/CHANGES
+++ b/CHANGES
@@ -15,6 +15,11 @@ $ pip install --user --upgrade --pre libtmux
 
 <!-- To maintainers and contributors: Please add notes for the forthcoming version above -->
 
+### Bug fix
+
+- `Server.new_session`: Fix handling of environmental variables passed to new
+  sessions. Thank you @ppentchev! (#553)
+
 ## libtmux 0.40.0 (2024-12-20)
 
 _Maintenance only, no bug fixes or new features_
diff --git a/tests/test_server.py b/tests/test_server.py
index de337aa77..511c7d951 100644
--- a/tests/test_server.py
+++ b/tests/test_server.py
@@ -134,11 +134,13 @@ def test_new_session_shell(server: Server) -> None:
 
 
 def test_new_session_shell_env(server: Server) -> None:
-    """Verify ``Server.new_session`` creates valid session running w/ command."""
+    """Verify ``Server.new_session`` creates valid session running w/ command (#553)."""
     cmd = "sleep 1m"
     env = dict(os.environ)
     mysession = server.new_session(
-        "test_new_session_env", window_command=cmd, environment=env
+        "test_new_session_env",
+        window_command=cmd,
+        environment=env,
     )
     time.sleep(0.1)
     window = mysession.windows[0]