diff --git a/Lib/email/_header_value_parser.py b/Lib/email/_header_value_parser.py
index f396f4f9b32a9a8..9c1f99b1615f61c 100644
--- a/Lib/email/_header_value_parser.py
+++ b/Lib/email/_header_value_parser.py
@@ -155,7 +155,7 @@ def all_defects(self):
         return sum((x.all_defects for x in self), self.defects)
 
     def startswith_fws(self):
-        return self[0].startswith_fws()
+        return self and self[0].startswith_fws()
 
     as_ew_allowed = True
 
diff --git a/Misc/NEWS.d/next/Library/2026-10-18-05-47-56.gh-issue-159621.Uspw6i.rst b/Misc/NEWS.d/next/Library/2026-10-18-05-47-56.gh-issue-159621.Uspw6i.rst
new file mode 100644
index 000000000000000..e744bfe1b75579f
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-10-18-05-47-56.gh-issue-159621.Uspw6i.rst
@@ -0,0 +1,2 @@
+Fix an :exc:`IndexError` in :mod:`email` when folding address headers
+containing empty comments.