1 files changed, 2 insertions, 1 deletions
diff --git a/sphinx/domains/index.py b/sphinx/domains/index.py
index fd1a76613..9ecfae439 100644
--- a/sphinx/domains/index.py
+++ b/sphinx/domains/index.py
@@ -20,6 +20,7 @@ from sphinx.environment import BuildEnvironment
 from sphinx.util import logging, split_index_msg
 from sphinx.util.docutils import ReferenceRole, SphinxDirective
 from sphinx.util.nodes import process_index_entry
+from sphinx.util.typing import OptionSpec
 
 if TYPE_CHECKING:
     from sphinx.application import Sphinx
@@ -67,7 +68,7 @@ class IndexDirective(SphinxDirective):
     required_arguments = 1
     optional_arguments = 0
     final_argument_whitespace = True
-    option_spec = {
+    option_spec: OptionSpec = {
         'name': directives.unchanged,
     }