diff --git a/cssselect/parser.py b/cssselect/parser.py
index f969769..2c0a55e 100644
--- a/cssselect/parser.py
+++ b/cssselect/parser.py
@@ -919,7 +919,7 @@ def _compile(pattern: str) -> MatchFunc:
 
 def _replace_unicode(match: re.Match[str]) -> str:
     codepoint = int(match.group(1), 16)
-    if codepoint > sys.maxunicode:
+    if codepoint > sys.maxunicode or 0xD800 <= codepoint <= 0xDFFF:
         codepoint = 0xFFFD
     return chr(codepoint)
 
diff --git a/tests/test_cssselect.py b/tests/test_cssselect.py
index dc67bb7..a1164e7 100644
--- a/tests/test_cssselect.py
+++ b/tests/test_cssselect.py
@@ -213,6 +213,7 @@ def test_pseudo_repr(css: str) -> str:
         assert parse_one("*") == ("Element[*]", None)
         assert parse_one(":empty") == ("Pseudo[Element[*]:empty]", None)
         assert parse_one(":scope") == ("Pseudo[Element[*]:scope]", None)
+        assert parse_one(":\\DDDD") == ("Pseudo[Element[*]:\ufffd]", None)
 
         # Special cases for CSS 2.1 pseudo-elements
         assert parse_one(":BEfore") == ("Element[*]", "before")