diff --git a/pyglossary/glossary_types.py b/pyglossary/glossary_types.py
index ab413581a..eb52c47b9 100644
--- a/pyglossary/glossary_types.py
+++ b/pyglossary/glossary_types.py
@@ -201,7 +201,7 @@ def wordTitleStr(
 		self,
 		word: str,
 		sample: str = "",
-		_class: str = "",
+		class_: str = "",
 	) -> str: ...
 
 	def getConfig(self, name: str, default: str | None) -> str | None: ...
diff --git a/pyglossary/glossary_v2.py b/pyglossary/glossary_v2.py
index 5fe50dbfa..c3a1ff1a9 100644
--- a/pyglossary/glossary_v2.py
+++ b/pyglossary/glossary_v2.py
@@ -565,7 +565,7 @@ def wordTitleStr(
 		self,
 		word: str,
 		sample: str = "",
-		_class: str = "",
+		class_: str = "",
 	) -> str:
 		"""
 		Return title tag for words.
@@ -587,8 +587,8 @@ def wordTitleStr(
 		if not sample:
 			sample = word
 		tag = self.titleTag(sample)
-		if _class:
-			return f'<{tag} class="{_class}">{word}</{tag}><br>'
+		if class_:
+			return f'<{tag} class="{class_}">{word}</{tag}><br>'
 		return f"<{tag}>{word}</{tag}><br>"
 
 	def getConfig(self, name: str, default: str | None) -> str | None:
diff --git a/pyglossary/plugins/html_dir.py b/pyglossary/plugins/html_dir.py
index 050f85258..cca7fcf6a 100644
--- a/pyglossary/plugins/html_dir.py
+++ b/pyglossary/plugins/html_dir.py
@@ -492,7 +492,7 @@ def addLinks(text: str, pos: int) -> None:
 				title = glos.wordTitleStr(
 					wordSep.join(words),
 					sample=entry.l_word[0],
-					_class="headword",
+					class_="headword",
 				)
 
 			if not title:
diff --git a/tests/deprecated/glossary_test.py b/tests/deprecated/glossary_test.py
index e32faa85d..ed9310234 100644
--- a/tests/deprecated/glossary_test.py
+++ b/tests/deprecated/glossary_test.py
@@ -1065,7 +1065,7 @@ def test_wordTitleStr_b1(self):
 	def test_wordTitleStr_b2(self):
 		glos = self.glos = Glossary()
 		self.assertEqual(
-			glos.wordTitleStr("test1", _class="headword"),
+			glos.wordTitleStr("test1", class_="headword"),
 			'<b class="headword">test1</b><br>',
 		)
 
diff --git a/tests/glossary_v2_test.py b/tests/glossary_v2_test.py
index 51f18c73b..b66cfcf1a 100644
--- a/tests/glossary_v2_test.py
+++ b/tests/glossary_v2_test.py
@@ -950,7 +950,7 @@ def test_wordTitleStr_b1(self):
 	def test_wordTitleStr_b2(self):
 		glos = self.glos = Glossary()
 		self.assertEqual(
-			glos.wordTitleStr("test1", _class="headword"),
+			glos.wordTitleStr("test1", class_="headword"),
 			'<b class="headword">test1</b><br>',
 		)