diff --git a/sphinx/domains/cpp.py b/sphinx/domains/cpp.py
index ea41f81c7..59d53463f 100644
--- a/sphinx/domains/cpp.py
+++ b/sphinx/domains/cpp.py
@@ -6044,7 +6044,7 @@ class CPPXRefRole(XRefRole):
         if not has_explicit_title:
             # major hax: replace anon names via simple string manipulation.
             # Can this actually fail?
-            title = _anon_identifier_re.sub("[anonymous]", title)
+            title = _anon_identifier_re.sub("[anonymous]", str(title))
 
         if refnode['reftype'] == 'any':
             # Assume the removal part of fix_parens for :any: refs.