From dfc5543b90d7da91f796d0e57b325e55917ebcd0 Mon Sep 17 00:00:00 2001
From: h1whelan <h1whelan@users.noreply.github.com>
Date: Mon, 30 Mar 2026 10:17:53 +0100
Subject: [PATCH 1/2] Fix: strip UTF-8 BOM from .env files to prevent silent
 first-variable loss

When a .env file is saved with a UTF-8 BOM (common with JetBrains IDEs
on Windows), the BOM character (\ufeff) was prepended to the first
variable name, making it silently inaccessible via its intended key.

Strip the BOM in Reader.__init__ so all variables are parsed correctly
regardless of whether the file contains a BOM.

Fixes #637

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
---
 src/dotenv/parser.py |  2 +-
 tests/test_parser.py | 29 +++++++++++++++++++++++++++++
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/src/dotenv/parser.py b/src/dotenv/parser.py
index eb100b47..66773604 100644
--- a/src/dotenv/parser.py
+++ b/src/dotenv/parser.py
@@ -68,7 +68,7 @@ class Error(Exception):
 
 class Reader:
     def __init__(self, stream: IO[str]) -> None:
-        self.string = stream.read()
+        self.string = stream.read().removeprefix("\ufeff")
         self.position = Position.start()
         self.mark = Position.start()
 
diff --git a/tests/test_parser.py b/tests/test_parser.py
index 43386e5a..4ec5a5af 100644
--- a/tests/test_parser.py
+++ b/tests/test_parser.py
@@ -545,6 +545,35 @@
                 ),
             ],
         ),
+        # UTF-8 BOM at the start of the file should be stripped
+        (
+            "\ufeffa=b",
+            [
+                Binding(
+                    key="a",
+                    value="b",
+                    original=Original(string="a=b", line=1),
+                    error=False,
+                )
+            ],
+        ),
+        (
+            "\ufeffa=b\nc=d",
+            [
+                Binding(
+                    key="a",
+                    value="b",
+                    original=Original(string="a=b\n", line=1),
+                    error=False,
+                ),
+                Binding(
+                    key="c",
+                    value="d",
+                    original=Original(string="c=d", line=2),
+                    error=False,
+                ),
+            ],
+        ),
     ],
 )
 def test_parse_stream(test_input, expected):

From 640311b11271e487b8fc27707267ad28369a0a51 Mon Sep 17 00:00:00 2001
From: Saurabh Kumar <theskumar@users.noreply.github.com>
Date: Mon, 20 Apr 2026 01:07:33 +0530
Subject: [PATCH 2/2] docs: add changelog entry for BOM fix

---
 CHANGELOG.md | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index ee732346..fa81cc6e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,7 +7,9 @@ project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
 
-- ...
+### Fixed
+
+- Strip a leading UTF-8 BOM from `.env` file contents so the first variable is no longer silently lost when the file is saved with BOM (e.g. by some JetBrains IDEs on Windows) by [@h1whelan] in [#640]
 
 ## [1.2.2] - 2026-03-01
 
@@ -432,6 +434,7 @@ os.PathLike]` instead of just `os.PathLike` (#347 by [@bbc2]).
 [#563]: https://github.com/theskumar/python-dotenv/pull/563
 [#497]: https://github.com/theskumar/python-dotenv/pull/497
 [#161]: https://github.com/theskumar/python-dotenv/issues/161
+[#640]: https://github.com/theskumar/python-dotenv/pull/640
 [790c5c0]: https://github.com/theskumar/python-dotenv/commit/790c5c02991100aa1bf41ee5330aca75edc51311
 
 <!-- contributors -->
@@ -460,6 +463,7 @@ os.PathLike]` instead of just `os.PathLike` (#347 by [@bbc2]).
 [@gergelyk]: https://github.com/gergelyk
 [@gongqingkui]: https://github.com/gongqingkui
 [@greyli]: https://github.com/greyli
+[@h1whelan]: https://github.com/h1whelan
 [@harveer07]: https://github.com/harveer07
 [@jadutter]: https://github.com/jadutter
 [@jankislinger]: https://github.com/jankislinger