diff --git a/isort/api.py b/isort/api.py
index 58367f3e0..873d77bfd 100644
--- a/isort/api.py
+++ b/isort/api.py
@@ -398,7 +398,7 @@ def _sort_imports(
         else:
             stripped_line = line.strip()
             if stripped_line and not line_separator:
-                line_separator = line[len(line.rstrip()):]
+                line_separator = line[len(line.rstrip()) :]
 
             for file_skip_comment in FILE_SKIP_COMMENTS:
                 if file_skip_comment in line:
diff --git a/tests/test_regressions.py b/tests/test_regressions.py
index 8b751e318..6910f9914 100644
--- a/tests/test_regressions.py
+++ b/tests/test_regressions.py
@@ -231,8 +231,8 @@ def test_windows_newline_issue_1277():
     See: https://github.com/timothycrosley/isort/issues/1277
     """
     assert (
-        isort.code("\ndef main():\r\n    import time\r\n\n    import sys\r\n") ==
-        "\ndef main():\r\n    import sys\r\n    import time\r\n"
+        isort.code("\ndef main():\r\n    import time\r\n\n    import sys\r\n")
+        == "\ndef main():\r\n    import sys\r\n    import time\r\n"
     )