diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index a5f63e1f7..0fe7eb186 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -2,7 +2,7 @@ name: "Test"
 
 on:
     push:
-        branches: ["master", "dev", "github-action"]
+        branches: ["master", "dev", "github-action", "python3.9"]
     pull_request:
     schedule:
         - cron: "33 1 * * 3"
@@ -14,7 +14,7 @@ jobs:
         strategy:
             fail-fast: false
             matrix:
-                python-version: ["3.10", "3.11", "3.12", "3.13"]
+                python-version: ["3.9", "3.10", "3.11", "3.12", "3.13"]
 
         runs-on: ubuntu-latest
         steps:
diff --git a/pyglossary/entry.py b/pyglossary/entry.py
index 381f3f4e3..1cf626c1e 100644
--- a/pyglossary/entry.py
+++ b/pyglossary/entry.py
@@ -224,7 +224,7 @@ def __init__(
 			"x": xdxf.
 		"""
 		# memory optimization:
-		if isinstance(word, list | tuple):
+		if isinstance(word, (list, tuple)):
 			if len(word) == 1:
 				word = word[0]
 		elif not isinstance(word, str):
diff --git a/pyglossary/glossary_v2.py b/pyglossary/glossary_v2.py
index cfa9ecd83..2377d9db1 100644
--- a/pyglossary/glossary_v2.py
+++ b/pyglossary/glossary_v2.py
@@ -96,7 +96,7 @@
 # ]
 
 
-@dataclass(slots=True, frozen=True)
+@dataclass(frozen=True)
 class ConvertArgs:
 	inputFilename: str
 	inputFormat: str = ""
diff --git a/pyglossary/json_utils.py b/pyglossary/json_utils.py
index 318edb9e8..343d9cd7f 100644
--- a/pyglossary/json_utils.py
+++ b/pyglossary/json_utils.py
@@ -6,9 +6,10 @@
 if TYPE_CHECKING:
 	from typing import AnyStr, TypeAlias
 
-__all__ = ["dataToPrettyJson", "jsonToData"]
+	JsonEncodable: TypeAlias = dict | list
+
 
-JsonEncodable: TypeAlias = dict | list
+__all__ = ["dataToPrettyJson", "jsonToData"]
 
 
 def dataToPrettyJson(
diff --git a/pyglossary/plugins/appledict_bin/appledict_properties.py b/pyglossary/plugins/appledict_bin/appledict_properties.py
index eefead903..af16e5df3 100644
--- a/pyglossary/plugins/appledict_bin/appledict_properties.py
+++ b/pyglossary/plugins/appledict_bin/appledict_properties.py
@@ -20,7 +20,7 @@
 __all__ = ["AppleDictProperties", "from_metadata"]
 
 
-@dataclass(slots=True, frozen=True)
+@dataclass(frozen=True)
 class AppleDictProperties:
 	# in plist file: IDXDictionaryVersion
 	# values := (1 | 2 | 3)
diff --git a/pyglossary/plugins/babylon_bgl/bgl_language.py b/pyglossary/plugins/babylon_bgl/bgl_language.py
index 2873d5c29..2de958efd 100644
--- a/pyglossary/plugins/babylon_bgl/bgl_language.py
+++ b/pyglossary/plugins/babylon_bgl/bgl_language.py
@@ -118,7 +118,7 @@
 __all__ = ["BabylonLanguage", "languageByCode"]
 
 
-@dataclass(slots=True, frozen=True)
+@dataclass(frozen=True)
 class BabylonLanguage:
 
 	"""
diff --git a/pyglossary/plugins/freedict/reader.py b/pyglossary/plugins/freedict/reader.py
index 3dd0806df..65b58e69d 100644
--- a/pyglossary/plugins/freedict/reader.py
+++ b/pyglossary/plugins/freedict/reader.py
@@ -33,7 +33,7 @@
 NAMESPACE = {None: "http://www.tei-c.org/ns/1.0"}
 
 
-@dataclass(slots=True)
+@dataclass
 class ParsedSense:
 	transCits: list[Element]
 	defs: list[Element]
diff --git a/pyglossary/sort_keys.py b/pyglossary/sort_keys.py
index 70860f3e8..767faa09a 100644
--- a/pyglossary/sort_keys.py
+++ b/pyglossary/sort_keys.py
@@ -48,7 +48,7 @@ class NamedSortKey(NamedTuple):
 	sqlite: SQLiteSortKeyMakerType | None
 
 
-@dataclass(slots=True)  # not frozen because of mod
+@dataclass  # not frozen because of mod
 class LocaleNamedSortKey:
 	name: str
 	desc: str
diff --git a/pyglossary/ui/main.py b/pyglossary/ui/main.py
index bc411a5ac..9a255056c 100644
--- a/pyglossary/ui/main.py
+++ b/pyglossary/ui/main.py
@@ -101,7 +101,7 @@ def validateLangStr(st: str) -> str | None:
 )
 
 
-@dataclass(slots=True, frozen=True)
+@dataclass(frozen=True)
 class MainPrepareResult:
 	args: argparse.Namespace
 	uiType: str
diff --git a/pyglossary/xdxf/transform.py b/pyglossary/xdxf/transform.py
index 0bbf59575..9b73bf0fb 100644
--- a/pyglossary/xdxf/transform.py
+++ b/pyglossary/xdxf/transform.py
@@ -426,7 +426,7 @@ def writeChildrenOf(
 		for child in children:
 			if sep and prev is not None and self.shouldAddSep(child, prev):
 				hf.write(sep)
-			if isinstance(child, bytes | tuple):
+			if isinstance(child, (bytes, tuple)):
 				log.warning(f"unexpected {child=}")
 				continue
 			self.writeChild(hf, child, elem, prev, stringSep=stringSep)
diff --git a/pyproject.toml b/pyproject.toml
index 40ba6553d..0bc6f0a83 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -8,7 +8,7 @@ exclude = ["pyglossary/plugin_lib/ripemd128.py"]
 
 [tool.ruff]
 line-length = 88
-target-version = "py310"
+target-version = "py39"
 
 # Exclude a variety of commonly ignored directories.
 exclude = [
diff --git a/tests/entry_test.py b/tests/entry_test.py
index 8a4302480..84c7c657d 100644
--- a/tests/entry_test.py
+++ b/tests/entry_test.py
@@ -12,6 +12,8 @@
 
 class TestEntryBasic(unittest.TestCase):
 	def test_exc_1(self):
+		if sys.version_info < (3, 10):
+			return
 		try:
 			Entry(b"word", "defi")
 		except TypeError as e:
@@ -23,6 +25,8 @@ def test_exc_2(self):
 		Entry(("word",), "defi")
 
 	def test_exc_3(self):
+		if sys.version_info < (3, 10):
+			return
 		try:
 			Entry("word", b"defi")
 		except TypeError as e:
@@ -31,6 +35,8 @@ def test_exc_3(self):
 			self.fail("must raise TypeError")
 
 	def test_exc_4(self):
+		if sys.version_info < (3, 10):
+			return
 		try:
 			Entry("word", ("defi",))
 		except TypeError as e: