diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index caaf0034..491236b3 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -18,6 +18,8 @@ jobs:
             runs-on: ubuntu-latest
           - name: macOS
             runs-on: macos-latest
+          - name: Windows
+            runs-on: windows-latest
         python:
           - name: CPython 2.7
             tox: py27
@@ -46,6 +48,14 @@ jobs:
         task:
           - name: Test
             tox: tests
+        exclude:
+          # Twisted and thus trial do not work on Windows with CPython 3.9.
+          # This will be fixed with the next release.
+          # https://twistedmatrix.com/trac/ticket/10027
+          - python:
+              tox: py39
+            os:
+              name: Windows
 
     steps:
     - uses: actions/checkout@v2
diff --git a/src/towncrier/_writer.py b/src/towncrier/_writer.py
index 65c9324e..1a2c31dc 100644
--- a/src/towncrier/_writer.py
+++ b/src/towncrier/_writer.py
@@ -8,6 +8,7 @@
 
 from __future__ import absolute_import, division
 
+import io
 import os
 
 
@@ -21,8 +22,8 @@ def append_to_newsfile(
         if not os.path.exists(news_file):
             existing_content = u""
         else:
-            with open(news_file, "rb") as f:
-                existing_content = f.read().decode("utf8")
+            with io.open(news_file, "r", encoding="utf8") as f:
+                existing_content = f.read()
         existing_content = existing_content.split(start_line, 1)
     else:
         existing_content = [u""]
diff --git a/src/towncrier/check.py b/src/towncrier/check.py
index cdd06d6b..3979fa45 100644
--- a/src/towncrier/check.py
+++ b/src/towncrier/check.py
@@ -48,12 +48,10 @@ def __main(comparewith, directory, config):
         click.echo("On trunk, or no diffs, so no newsfragment required.")
         sys.exit(0)
 
-    files = set(
-        map(
-            lambda x: os.path.join(base_directory, x),
-            files_changed.strip().split(os.linesep),
-        )
-    )
+    files = {
+        os.path.normpath(os.path.join(base_directory, path))
+        for path in files_changed.strip().splitlines()
+    }
 
     click.echo("Looking at these files:")
     click.echo("----")
@@ -72,14 +70,15 @@ def __main(comparewith, directory, config):
         )
         fragment_directory = "newsfragments"
 
-    fragments = set(
-        find_fragments(
+    fragments = {
+        os.path.normpath(path)
+        for path in find_fragments(
             fragment_base_directory,
             config["sections"],
             fragment_directory,
             config["types"],
         )[1]
-    )
+    }
     fragments_in_branch = fragments & files
 
     if not fragments_in_branch:
diff --git a/src/towncrier/newsfragments/287.misc.rst b/src/towncrier/newsfragments/287.misc.rst
new file mode 100644
index 00000000..e69de29b
diff --git a/src/towncrier/test/test_settings.py b/src/towncrier/test/test_settings.py
index 9fbc987f..6565ca07 100644
--- a/src/towncrier/test/test_settings.py
+++ b/src/towncrier/test/test_settings.py
@@ -169,7 +169,10 @@ def test_missing_template(self):
             load_config(temp)
 
         self.assertEqual(
-            str(e.exception), "The template file '%s/foo.rst' does not exist." % (temp,)
+            str(e.exception),
+            "The template file '{}' does not exist.".format(
+                os.path.normpath(os.path.join(temp, "foo.rst")),
+            )
         )
 
     def test_missing_template_in_towncrier(self):
diff --git a/tox.ini b/tox.ini
index 8c605254..b4f0ad24 100644
--- a/tox.ini
+++ b/tox.ini
@@ -35,7 +35,9 @@ commands =
    coverage --version
    {envbindir}/trial --version
    coverage erase
-   coverage run -p {envbindir}/trial {posargs:towncrier}
+   # `coverage run` tries to act like Python so we use `--module` instead of
+   # specifying the entry point script in `{envbindir}`.
+   coverage run -p --module twisted.trial {posargs:towncrier}
    coverage combine -a
 
 [testenv:cov-report]