diff --git a/src/fromager/dependencies.py b/src/fromager/dependencies.py
index d80899e8..18dcdbef 100644
--- a/src/fromager/dependencies.py
+++ b/src/fromager/dependencies.py
@@ -574,7 +574,7 @@ def _write_requirements_file(
     filename: pathlib.Path,
 ) -> None:
     with open(filename, "w") as f:
-        for r in requirements:
+        for r in sorted(requirements, key=str):
             f.write(f"{r}\n")
 
 
diff --git a/tests/test_dependencies.py b/tests/test_dependencies.py
index 6f83a93e..34a68ee8 100644
--- a/tests/test_dependencies.py
+++ b/tests/test_dependencies.py
@@ -179,6 +179,20 @@ def test_get_build_system_dependencies_cached(
     assert results == set([Requirement("foo==1.0")])
 
 
+def test_write_requirements_file_sorted(tmp_path: pathlib.Path) -> None:
+    """Verify the file content does not depend on input or set order."""
+    req_file = tmp_path / "build-system-requirements.txt"
+    requirements = [
+        Requirement("setuptools>=42"),
+        Requirement("setuptools-scm[toml]>=3.4"),
+        Requirement("cython"),
+    ]
+    dependencies._write_requirements_file(requirements, req_file)
+    assert req_file.read_text() == (
+        "cython\nsetuptools-scm[toml]>=3.4\nsetuptools>=42\n"
+    )
+
+
 @patch("fromager.dependencies._write_requirements_file")
 @_clean_build_artifacts
 @pytest.mark.network