diff --git a/pre_commit_hooks/insert_license.py b/pre_commit_hooks/insert_license.py
index 887651d..42a01b1 100644
--- a/pre_commit_hooks/insert_license.py
+++ b/pre_commit_hooks/insert_license.py
@@ -143,7 +143,7 @@ def get_license_info(args) -> LicenseInfo:
     )
     if "|" in comment_prefix:
         comment_start, comment_prefix, comment_end = comment_prefix.split("|")
-    with open(args.license_filepath, encoding="utf8") as license_file:
+    with open(args.license_filepath, encoding="utf8", newline="") as license_file:
         plain_license = license_file.readlines()
 
     if args.use_current_year:
@@ -268,7 +268,7 @@ def _read_file_content(src_filepath):
         "ISO-8859-1",
     ):  # we could use the chardet library to support more encodings
         try:
-            with open(src_filepath, encoding=encoding) as src_file:
+            with open(src_filepath, encoding=encoding, newline="") as src_file:
                 return src_file.readlines(), encoding
         except UnicodeDecodeError as error:
             last_error = error
@@ -324,7 +324,7 @@ def license_not_found(  # pylint: disable=too-many-arguments
             + [license_info.eol]
             + src_file_content[index:]
         )
-        with open(src_filepath, "w", encoding=encoding) as src_file:
+        with open(src_filepath, "w", encoding=encoding, newline="") as src_file:
             src_file.write("".join(src_file_content))
         return True
     return False
@@ -458,7 +458,7 @@ def license_found(
         )
 
     if updated:
-        with open(src_filepath, "w", encoding=encoding) as src_file:
+        with open(src_filepath, "w", encoding=encoding, newline="") as src_file:
             src_file.write("".join(src_file_content))
 
     return updated
@@ -494,7 +494,7 @@ def fuzzy_license_found(
         ]
         + src_file_content[fuzzy_match_header_index:]
     )
-    with open(src_filepath, "w", encoding=encoding) as src_file:
+    with open(src_filepath, "w", encoding=encoding, newline="") as src_file:
         src_file.write("".join(src_file_content))
     return True
 
@@ -661,7 +661,8 @@ def get_license_candidate_string(candidate_array, license_info):
                         )
                 else:
                     in_license = True
-                    found_license_offset = current_offset  # We have no data :(. We start license immediately
+                    # We have no data :(. We start license immediately
+                    found_license_offset = current_offset
         else:
             if stripped_comment_end and stripped_line.startswith(stripped_comment_end):
                 break
diff --git a/tests/insert_license_test.py b/tests/insert_license_test.py
index c1ae7ee..2972849 100644
--- a/tests/insert_license_test.py
+++ b/tests/insert_license_test.py
@@ -8,12 +8,40 @@
 
 from .utils import chdir_to_test_resources, capture_stdout
 
+
 # pylint: disable=too-many-arguments
 
 
+def _convert_line_ending(file_path, new_line_endings):
+    for encoding in (
+        "utf8",
+        "ISO-8859-1",
+    ):  # we could use the chardet library to support more encodings
+        last_error = None
+        try:
+            with open(file_path, encoding=encoding, newline="") as f_in:
+                content = f_in.read()
+
+            with open(
+                file_path, "w", encoding=encoding, newline=new_line_endings
+            ) as f_out:
+                f_out.write(content)
+
+            return
+        except UnicodeDecodeError as error:
+            last_error = error
+    print(
+        f"Error while processing: {file_path} - file encoding is probably not supported"
+    )
+    if last_error is not None:  # Avoid mypy message
+        raise last_error
+    raise RuntimeError("Unexpected branch taken (_convert_line_ending)")
+
+
 @pytest.mark.parametrize(
     (
         "license_file_path",
+        "line_ending",
         "src_file_path",
         "comment_prefix",
         "new_src_file_expected",
@@ -22,13 +50,14 @@
         "extra_args",
     ),
     map(
-        lambda a: a[:1] + a[1],
+        lambda a: a[:2] + a[2],
         chain(
             product(  # combine license files with other args
                 (
                     "LICENSE_with_trailing_newline.txt",
                     "LICENSE_without_trailing_newline.txt",
                 ),
+                ("\n", "\r\n"),
                 (
                     (
                         "module_without_license.py",
@@ -209,10 +238,182 @@
                         True,
                         ["--use-current-year"],
                     ),
+                    (
+                        "module_without_license.py",
+                        "#",
+                        "module_with_license.py",
+                        "",
+                        True,
+                        None,
+                    ),
+                    ("module_without_license_skip.py", "#", None, "", False, None),
+                    ("module_with_license.py", "#", None, "", False, None),
+                    ("module_with_license_todo.py", "#", None, "", True, None),
+                    (
+                        "module_without_license.jinja",
+                        "{#||#}",
+                        "module_with_license.jinja",
+                        "",
+                        True,
+                        None,
+                    ),
+                    (
+                        "module_without_license_skip.jinja",
+                        "{#||#}",
+                        None,
+                        "",
+                        False,
+                        None,
+                    ),
+                    ("module_with_license.jinja", "{#||#}", None, "", False, None),
+                    ("module_with_license_todo.jinja", "{#||#}", None, "", True, None),
+                    (
+                        "module_without_license_and_shebang.py",
+                        "#",
+                        "module_with_license_and_shebang.py",
+                        "",
+                        True,
+                        None,
+                    ),
+                    (
+                        "module_without_license_and_shebang_skip.py",
+                        "#",
+                        None,
+                        "",
+                        False,
+                        None,
+                    ),
+                    ("module_with_license_and_shebang.py", "#", None, "", False, None),
+                    (
+                        "module_with_license_and_shebang_todo.py",
+                        "#",
+                        None,
+                        "",
+                        True,
+                        None,
+                    ),
+                    (
+                        "module_without_license.groovy",
+                        "//",
+                        "module_with_license.groovy",
+                        "",
+                        True,
+                        None,
+                    ),
+                    ("module_without_license_skip.groovy", "//", None, "", False, None),
+                    ("module_with_license.groovy", "//", None, "", False, None),
+                    ("module_with_license_todo.groovy", "//", None, "", True, None),
+                    (
+                        "module_without_license.css",
+                        "/*| *| */",
+                        "module_with_license.css",
+                        "",
+                        True,
+                        None,
+                    ),
+                    (
+                        "module_without_license_and_few_words.css",
+                        "/*| *| */",
+                        "module_with_license_and_few_words.css",
+                        "",
+                        True,
+                        None,
+                    ),  # Test fuzzy match does not match greedily
+                    (
+                        "module_without_license_skip.css",
+                        "/*| *| */",
+                        None,
+                        "",
+                        False,
+                        None,
+                    ),
+                    ("module_with_license.css", "/*| *| */", None, "", False, None),
+                    ("module_with_license_todo.css", "/*| *| */", None, "", True, None),
+                    (
+                        "main_without_license.cpp",
+                        "/*|\t| */",
+                        "main_with_license.cpp",
+                        "",
+                        True,
+                        None,
+                    ),
+                    (
+                        "main_iso8859_without_license.cpp",
+                        "/*|\t| */",
+                        "main_iso8859_with_license.cpp",
+                        "",
+                        True,
+                        None,
+                    ),
+                    (
+                        "module_without_license.txt",
+                        "",
+                        "module_with_license_noprefix.txt",
+                        "",
+                        True,
+                        None,
+                    ),
+                    (
+                        "module_without_license.py",
+                        "#",
+                        "module_with_license_nospace.py",
+                        "",
+                        True,
+                        ["--no-space-in-comment-prefix"],
+                    ),
+                    (
+                        "module_without_license.php",
+                        "/*| *| */",
+                        "module_with_license.php",
+                        "",
+                        True,
+                        ["--insert-license-after-regex", "^<\\?php$"],
+                    ),
+                    (
+                        "module_without_license.py",
+                        "#",
+                        "module_with_license_noeol.py",
+                        "",
+                        True,
+                        ["--no-extra-eol"],
+                    ),
+                    (
+                        "module_without_license.groovy",
+                        "//",
+                        "module_with_license.groovy",
+                        "",
+                        True,
+                        ["--use-current-year"],
+                    ),
+                    (
+                        "module_with_stale_year_in_license.py",
+                        "#",
+                        "module_with_year_range_in_license.py",
+                        "",
+                        True,
+                        ["--use-current-year"],
+                    ),
+                    (
+                        "module_with_stale_year_range_in_license.py",
+                        "#",
+                        "module_with_year_range_in_license.py",
+                        "",
+                        True,
+                        ["--use-current-year"],
+                    ),
+                    (
+                        "module_with_badly_formatted_stale_year_range_in_license.py",
+                        "#",
+                        "module_with_badly_formatted_stale_year_range_in_license.py",
+                        "module_with_badly_formatted_stale_year_range_in_license.py",
+                        True,
+                        ["--use-current-year"],
+                    ),
                 ),
             ),
             product(
                 ("LICENSE_with_year_range_and_trailing_newline.txt",),
+                ("\n", "\r\n"),
                 (
                     (
                         "module_without_license.groovy",
@@ -229,6 +430,7 @@
 )
 def test_insert_license(
     license_file_path,
+    line_ending,
     src_file_path,
     comment_prefix,
     new_src_file_expected,
@@ -241,6 +443,7 @@ def test_insert_license(
     with chdir_to_test_resources():
         path = tmpdir.join(src_file_path)
         shutil.copy(src_file_path, path.strpath)
+        _convert_line_ending(path.strpath, line_ending)
         args = [
             "--license-filepath",
             license_file_path,
@@ -257,7 +460,7 @@ def test_insert_license(
 
         if new_src_file_expected:
             with open(
-                new_src_file_expected, encoding=encoding
+                new_src_file_expected, encoding=encoding, newline=line_ending
             ) as expected_content_file:
                 expected_content = expected_content_file.read()
                 if "--use-current-year" in args:
@@ -315,18 +518,20 @@ def test_insert_license_current_year_already_there(
 @pytest.mark.parametrize(
     (
         "license_file_path",
+        "line_ending",
         "src_file_path",
         "comment_style",
         "new_src_file_expected",
         "fail_check",
     ),
     map(
-        lambda a: a[:1] + a[1],
+        lambda a: a[:2] + a[2],
         product(  # combine license files with other args
             (
                 "LICENSE_with_trailing_newline.txt",
                 "LICENSE_without_trailing_newline.txt",
             ),
+            ("\n", "\r\n"),
             (
                 (
                     "module_without_license.jinja",
@@ -393,6 +598,7 @@ def test_insert_license_current_year_already_there(
 )
 def test_fuzzy_match_license(
     license_file_path,
+    line_ending,
     src_file_path,
     comment_style,
     new_src_file_expected,
@@ -402,6 +608,7 @@ def test_fuzzy_match_license(
     with chdir_to_test_resources():
         path = tmpdir.join("src_file_path")
         shutil.copy(src_file_path, path.strpath)
+        _convert_line_ending(path.strpath, line_ending)
         args = [
             "--license-filepath",
             license_file_path,
@@ -470,6 +677,7 @@ def test_is_license_present(src_file_content, expected_index, match_years_strict
 @pytest.mark.parametrize(
     (
         "license_file_path",
+        "line_ending",
         "src_file_path",
         "comment_style",
         "fuzzy_match",
@@ -478,12 +686,13 @@ def test_is_license_present(src_file_content, expected_index, match_years_strict
         "use_current_year",
     ),
     map(
-        lambda a: a[:1] + a[1],
+        lambda a: a[:2] + a[2],
         product(  # combine license files with other args
             (
                 "LICENSE_with_trailing_newline.txt",
                 "LICENSE_without_trailing_newline.txt",
             ),
+            ("\n", "\r\n"),
             (
                 (
                     "module_with_license.css",
@@ -625,6 +834,7 @@ def test_is_license_present(src_file_content, expected_index, match_years_strict
 )
 def test_remove_license(
     license_file_path,
+    line_ending,
     src_file_path,
     comment_style,
     fuzzy_match,
@@ -636,6 +846,7 @@ def test_remove_license(
     with chdir_to_test_resources():
         path = tmpdir.join("src_file_path")
         shutil.copy(src_file_path, path.strpath)
+        _convert_line_ending(path.strpath, line_ending)
         argv = [
             "--license-filepath",
             license_file_path,