diff --git a/sphinx/domains/std.py b/sphinx/domains/std.py
index d08c65668e6..65f95f1b896 100644
--- a/sphinx/domains/std.py
+++ b/sphinx/domains/std.py
@@ -244,6 +244,8 @@ def add_target_and_index(self, firstname: str, sig: str, signode: desc_signature
         else:
             descr = _('command line option')
         for option in sig.split(', '):
+            # remove trailing part followed by equal symbol
+            option = option.split('=')[0]
             entry = '; '.join([descr, option])
             self.indexnode['entries'].append(('pair', entry, signode['ids'][0], '', None))
 
diff --git a/tests/test_domain_std.py b/tests/test_domain_std.py
index c464ea00841..849f3bb87e6 100644
--- a/tests/test_domain_std.py
+++ b/tests/test_domain_std.py
@@ -328,7 +328,7 @@ def test_cmdoption_for_None(app):
     text = (".. program:: ls\n"
             ".. program:: None\n"
             "\n"
-            ".. option:: -l\n")
+            ".. option:: -l=foo|bar\n")
     domain = app.env.get_domain('std')
     doctree = restructuredtext.parse(app, text)
     assert_node(doctree, (addnodes.index,