diff --git a/sphinx/writers/html5.py b/sphinx/writers/html5.py
index c8458f2f106..faa37180633 100644
--- a/sphinx/writers/html5.py
+++ b/sphinx/writers/html5.py
@@ -56,6 +56,10 @@ class HTML5Translator(SphinxTranslator, BaseTranslator):
     """
 
     builder: "StandaloneHTMLBuilder" = None
+    # Override docutils.writers.html5_polyglot:HTMLTranslator
+    # otherwise, nodes like <inline classes="s">...</inline> will be
+    # converted to <s>...</s> by `visit_inline`.
+    self.supported_inline_tags = set()
 
     def __init__(self, document: nodes.document, builder: Builder) -> None:
         super().__init__(document, builder)
@@ -70,10 +74,6 @@ def __init__(self, document: nodes.document, builder: Builder) -> None:
         self._table_row_indices = [0]
         self._fieldlist_row_indices = [0]
         self.required_params_left = 0
-        # Override docutils.writers.html5_polyglot:HTMLTranslator
-        # otherwise, nodes like <inline classes="s">...</inline> will be
-        # converted to <s>...</s> by `visit_inline`.
-        self.supported_inline_tags = set()
 
     def visit_start_of_file(self, node: Element) -> None:
         # only occurs in the single-file builder