diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index b7cf1f03a..257c43e68 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -14,11 +14,13 @@ jobs:
     strategy:
       matrix:
         os:
-          - ubuntu-latest
-          - windows-latest
-          - macos-latest
-          - macos-13
+          - ubuntu-22.04
+          - ubuntu-20.04
+          - windows-2022
+          - windows-2019
           - macos-14
+          - macos-13
+          - macos-12
     steps:
       - uses: actions/checkout@v4
 
@@ -26,6 +28,11 @@ jobs:
         uses: ./
         id: postgres
 
+      - name: Run setup-python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.10"
+
       - name: Run tests
         run: |
           python3 -m pip install --upgrade pip pytest psycopg furl
@@ -57,6 +64,11 @@ jobs:
           port: 34837
         id: postgres
 
+      - name: Run setup-python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.10"
+
       - name: Run tests
         run: |
           python3 -m pip install --upgrade pip pytest psycopg furl
diff --git a/action.yml b/action.yml
index ee399a427..d63da77a1 100644
--- a/action.yml
+++ b/action.yml
@@ -64,6 +64,18 @@ runs:
         export PGDATA="$RUNNER_TEMP/pgdata"
         export PWFILE="$RUNNER_TEMP/pwfile"
 
+        DEFAULT_ENCODING="UTF-8"
+        DEFAULT_LOCALE="en_US.$DEFAULT_ENCODING"
+
+        # Unfortunately, Windows Server 2019 doesn't understand locale
+        # specified in the format defined by the POSIX standard, i.e.
+        # <language>_<country>.<encoding>. Therefore, we have to convert it
+        # into something it can swallow, i.e. <language>-<country>.
+        if [[ "$RUNNER_OS" == "Windows" && "$(wmic os get Caption)" == *"2019"* ]]; then
+          DEFAULT_LOCALE="${DEFAULT_LOCALE%%.*}"
+          DEFAULT_LOCALE="${DEFAULT_LOCALE//_/-}"
+        fi
+
         # Unfortunately 'initdb' could only receive a password via file on disk
         # or prompt to enter on. Prompting is not an option since we're running
         # in non-interactive mode.
@@ -82,8 +94,8 @@ runs:
           --username="${{ inputs.username }}" \
           --pwfile="$PWFILE" \
           --auth="scram-sha-256" \
-          --encoding="UTF-8" \
-          --locale="en_US.UTF-8" \
+          --encoding="$DEFAULT_ENCODING" \
+          --locale="$DEFAULT_LOCALE" \
           --no-instructions
 
         # Do not create unix sockets since they are created by default in the
diff --git a/test_action.py b/test_action.py
index a1f4540ea..f84149f6b 100644
--- a/test_action.py
+++ b/test_action.py
@@ -12,6 +12,24 @@
 ConnectionFactory = t.Callable[[str], psycopg.Connection]
 
 
+@pytest.fixture(scope="function")
+def is_windows() -> bool:
+    """Returns True if running on Windows."""
+
+    return os.name == "nt"
+
+
+@pytest.fixture(scope="function")
+def is_windows_server_2019(is_windows: bool) -> bool:
+    """Returns True if running on Windows Server 2019."""
+
+    if not is_windows:
+        return False
+
+    windows_caption = subprocess.check_output(["wmic", "os", "get", "Caption"], text=True)
+    return "Windows Server 2019" in windows_caption
+
+
 @pytest.fixture(scope="function")
 def connection_uri() -> str:
     """Read and return connection URI from environment."""
@@ -57,35 +75,40 @@ def connection(
     raise RuntimeError("f{request.param}: unknown value")
 
 
-def test_connection_uri(connection_uri):
+def test_connection_uri(connection_uri: str):
     """Test that CONNECTION_URI matches EXPECTED_CONNECTION_URI."""
 
     assert connection_uri == os.getenv("EXPECTED_CONNECTION_URI")
 
 
-def test_service_name(service_name):
+def test_service_name(service_name: str):
     """Test that SERVICE_NAME matches EXPECTED_SERVICE_NAME."""
 
     assert service_name == os.getenv("EXPECTED_SERVICE_NAME")
 
 
 def test_server_encoding(connection: psycopg.Connection):
-    """Test that PostgreSQL's encoding is 'UTF-8'."""
+    """Test that PostgreSQL's encoding matches the one we passed to initdb."""
 
     assert connection.execute("SHOW SERVER_ENCODING").fetchone()[0] == "UTF8"
 
 
-def test_locale(connection: psycopg.Connection):
-    """Test that PostgreSQL's locale is 'en_US.UTF-8'."""
+def test_locale(connection: psycopg.Connection, is_windows_server_2019: bool):
+    """Test that PostgreSQL's locale matches the one we paased to initdb."""
+
+    locale_exp = "en_US.UTF-8"
+
+    if is_windows_server_2019:
+        locale_exp = "en-US"
 
     lc_collate = connection.execute("SHOW LC_COLLATE").fetchone()[0]
     lc_ctype = connection.execute("SHOW LC_CTYPE").fetchone()[0]
 
-    assert locale.normalize(lc_collate) == "en_US.UTF-8"
-    assert locale.normalize(lc_ctype) == "en_US.UTF-8"
+    assert locale.normalize(lc_collate) == locale_exp
+    assert locale.normalize(lc_ctype) == locale_exp
 
 
-def test_environment_variables():
+def test_environment_variables(is_windows: bool):
     """Test that only expected 'PG*' variables are set."""
 
     pg_environ = {k: v for k, v in os.environ.items() if k.startswith("PG")}
@@ -96,7 +119,7 @@ def test_environment_variables():
     pg_servicefile_exp = pathlib.Path(os.environ["RUNNER_TEMP"], "pgdata", "pg_service.conf")
     assert pg_servicefile.resolve() == pg_servicefile_exp.resolve()
     
-    if os.name == "nt":
+    if is_windows:
         pg_environ_exp = {
             "PGBIN": "",
             "PGDATA": "",