diff --git a/rsconnect/pyproject.py b/rsconnect/pyproject.py
index d0b591d7..ddf77fec 100644
--- a/rsconnect/pyproject.py
+++ b/rsconnect/pyproject.py
@@ -97,7 +97,7 @@ def parse_pyproject_python_requires(pyproject_file: pathlib.Path) -> typing.Opti
 
     Returns None if the field is not found.
     """
-    content = pyproject_file.read_text()
+    content = pyproject_file.read_text(encoding="utf-8-sig")
     pyproject = tomllib.loads(content)
 
     return pyproject.get("project", {}).get("requires-python", None)
@@ -195,7 +195,7 @@ def read_tool_rsconnect(pyproject_file: pathlib.Path) -> typing.Mapping[str, typ
     missing or when required ``app_mode`` / ``entrypoint`` fields are absent or
     not non-empty strings.
     """
-    content = pyproject_file.read_text()
+    content = pyproject_file.read_text(encoding="utf-8-sig")
     pyproject = tomllib.loads(content)
 
     tool = pyproject.get("tool")
diff --git a/rsconnect/subprocesses/inspect_environment.py b/rsconnect/subprocesses/inspect_environment.py
index db4e13fa..b24bf851 100644
--- a/rsconnect/subprocesses/inspect_environment.py
+++ b/rsconnect/subprocesses/inspect_environment.py
@@ -281,7 +281,7 @@ def pyproject_dependencies(dirname: str, pyproject_filename: str):
         raise EnvironmentException(f"pyproject.toml not found: {pyproject_filename}")
 
     try:
-        with open(pyproject_path, "r", encoding="utf-8") as f:
+        with open(pyproject_path, "r", encoding="utf-8-sig") as f:
             pyproject = tomllib.loads(f.read())
     except Exception as exception:
         raise EnvironmentException(f"Error reading {pyproject_filename}: {exception}")
diff --git a/tests/test_environment.py b/tests/test_environment.py
index db75070e..ff841b64 100644
--- a/tests/test_environment.py
+++ b/tests/test_environment.py
@@ -208,7 +208,8 @@ def test_uv_lock_export(tmp_path):
     assert env.package_manager == "uv"
 
 
-def test_pyproject_dependencies(tmp_path):
+@pytest.mark.parametrize("encoding", ["utf-8", "utf-8-sig"])
+def test_pyproject_dependencies(tmp_path, encoding):
     project_dir = tmp_path / "project"
     project_dir.mkdir()
     (project_dir / "pyproject.toml").write_text(
@@ -220,7 +221,7 @@ def test_pyproject_dependencies(tmp_path):
         "    'annotated-types>=0.7.0',\n"
         "    'rsconnect-python==1.0.0',\n"
         "]\n",
-        encoding="utf-8",
+        encoding=encoding,
     )
 
     env = detect_environment(str(project_dir), requirements_file="pyproject.toml")
@@ -236,6 +237,14 @@ def test_pyproject_dependencies(tmp_path):
     assert env.package_manager == "pip"
 
 
+@pytest.mark.parametrize("encoding", ["utf-8", "utf-8-sig"])
+def test_pyproject_dependencies_invalid_toml(tmp_path, encoding):
+    (tmp_path / "pyproject.toml").write_text("[project\ndependencies =", encoding=encoding)
+
+    with pytest.raises(EnvironmentException, match="Error reading pyproject.toml"):
+        detect_environment(str(tmp_path), requirements_file="pyproject.toml")
+
+
 @pytest.mark.parametrize(
     "dependencies",
     [
diff --git a/tests/test_pyproject.py b/tests/test_pyproject.py
index 2863de0c..a43bda96 100644
--- a/tests/test_pyproject.py
+++ b/tests/test_pyproject.py
@@ -99,6 +99,14 @@ def test_pyprojecttoml_python_requires(project_dir, expected):
     assert parse_pyproject_python_requires(pyproject_file) == expected
 
 
+@pytest.mark.parametrize("encoding", ["utf-8", "utf-8-sig"])
+def test_pyprojecttoml_python_requires_encoding(tmp_path, encoding):
+    pyproject_file = tmp_path / "pyproject.toml"
+    pyproject_file.write_text('[project]\nname = "café"\nrequires-python = ">=3.8"\n', encoding=encoding)
+
+    assert parse_pyproject_python_requires(pyproject_file) == ">=3.8"
+
+
 @pytest.mark.parametrize(
     "project_dir, expected",
     [
diff --git a/tests/test_write_manifest_pyproject.py b/tests/test_write_manifest_pyproject.py
index d809f3ab..e51d0391 100644
--- a/tests/test_write_manifest_pyproject.py
+++ b/tests/test_write_manifest_pyproject.py
@@ -352,12 +352,19 @@ def test_write_manifest_pyproject_never_rewrites_explicit_requirements_source(
         pass
 
 
-def test_write_manifest_pyproject_unmocked_end_to_end(runner: CliRunner, project_dir: pathlib.Path):
+@pytest.mark.parametrize("encoding", ["utf-8", "utf-8-sig"])
+@pytest.mark.parametrize("command", ["pyproject", "api"])
+def test_write_manifest_pyproject_unmocked_end_to_end(
+    runner: CliRunner, project_dir: pathlib.Path, encoding: str, command: str
+):
     """Real environment inspection: default config must yield a deployable manifest."""
-    _write_pyproject(project_dir, _REQ_PYPROJECT)
+    (project_dir / "pyproject.toml").write_text(textwrap.dedent(_REQ_PYPROJECT), encoding=encoding)
     (project_dir / "app.py").write_text("app = None\n")
 
-    result = runner.invoke(cli, ["write-manifest", "pyproject", str(project_dir)])
+    args = ["write-manifest", command]
+    if command == "api":
+        args.extend(["-r", "pyproject.toml"])
+    result = runner.invoke(cli, [*args, str(project_dir)])
 
     assert result.exit_code == 0, result.output
     manifest = _read_manifest(project_dir)
@@ -514,8 +521,11 @@ def test_write_manifest_pyproject_errors_on_missing_pyproject(runner: CliRunner,
     assert "quickstart" in result.output.lower()
 
 
-def test_write_manifest_pyproject_errors_on_malformed_pyproject(runner: CliRunner, project_dir: pathlib.Path):
-    (project_dir / "pyproject.toml").write_text("[tool.rsconnect\napp_mode =")
+@pytest.mark.parametrize("encoding", ["utf-8", "utf-8-sig"])
+def test_write_manifest_pyproject_errors_on_malformed_pyproject(
+    runner: CliRunner, project_dir: pathlib.Path, encoding: str
+):
+    (project_dir / "pyproject.toml").write_text("[tool.rsconnect\napp_mode =", encoding=encoding)
     result = runner.invoke(cli, ["write-manifest", "pyproject", str(project_dir)])
     assert result.exit_code != 0
     assert "could not be parsed" in result.output