diff --git a/clang/tools/include-mapping/cppreference_parser.py b/clang/tools/include-mapping/cppreference_parser.py
--- a/clang/tools/include-mapping/cppreference_parser.py
+++ b/clang/tools/include-mapping/cppreference_parser.py
@@ -114,8 +114,17 @@
 
 
 def _ReadSymbolPage(path, name):
-  with open(path) as f:
-    return _ParseSymbolPage(f.read(), name)
+  try:
+    f = open(path)
+  except FileNotFoundError as e:
+    # Some entries exist in the index, but their corresponding pages have not
+    # been written yet (i.e., they are "red links"). When trying to open such
+    # a page, it redirects to a generic error page with "redlink=1" in the URL. 
+    if "redlink" in str(e):
+      return []
+    raise
+  with f:
+    return _ParseSymbolPage(f.read(), name) 
 
 
 def _GetSymbols(pool, root_dir, index_page_name, namespace, variants_to_accept):