diff --git a/contrib/schemagen/test_schemagen.py b/contrib/schemagen/test_schemagen.py
index afd71fe..15d3a67 100644
--- a/contrib/schemagen/test_schemagen.py
+++ b/contrib/schemagen/test_schemagen.py
@@ -49,5 +49,43 @@ class SchemagenEnumTest(unittest.TestCase):
         self.assertIn("enum class Role : int { admin, user, guest };", stdout)
 
 
+class SchemagenKeywordTest(unittest.TestCase):
+    def run_schemagen(self, schema, args=None):
+        """Run schemagen on a schema dict. Returns (returncode, stdout, stderr)."""
+        with tempfile.NamedTemporaryFile("w", suffix=".json", delete=False) as fp:
+            json.dump(schema, fp)
+            schema_path = fp.name
+        try:
+            cmd = [sys.executable, SCRIPT, schema_path]
+            if args:
+                cmd.extend(args)
+            result = subprocess.run(cmd, capture_output=True, text=True, check=False)
+            return result.returncode, result.stdout, result.stderr
+        finally:
+            os.unlink(schema_path)
+
+    def test_cpp20_keywords_are_sanitized(self):
+        """C++20 keywords used as JSON property names must be suffixed."""
+        keywords = [
+            "concept",
+            "consteval",
+            "constinit",
+            "co_await",
+            "co_return",
+            "co_yield",
+            "requires",
+            "module",
+            "import",
+        ]
+        schema = {"type": "object", "properties": {}}
+        for kw in keywords:
+            schema["properties"][kw] = {"type": "string"}
+        rc, stdout, stderr = self.run_schemagen(schema)
+        self.assertEqual(rc, 0, msg=stderr)
+        for kw in keywords:
+            self.assertIn(f"std::optional<std::string> {kw}_;", stdout)
+            self.assertNotIn(f"std::optional<std::string> {kw};", stdout)
+
+
 if __name__ == "__main__":
     unittest.main()
diff --git a/contrib/schemagen/weaseljson_schemagen.py b/contrib/schemagen/weaseljson_schemagen.py
index 1a7bab9..11b268b 100644
--- a/contrib/schemagen/weaseljson_schemagen.py
+++ b/contrib/schemagen/weaseljson_schemagen.py
@@ -133,9 +133,15 @@ _CPP_KEYWORDS = {
     "catch",
     "char",
     "class",
+    "concept",
     "const",
+    "consteval",
+    "constinit",
     "constexpr",
     "continue",
+    "co_await",
+    "co_return",
+    "co_yield",
     "decltype",
     "default",
     "delete",
@@ -152,9 +158,11 @@ _CPP_KEYWORDS = {
     "friend",
     "goto",
     "if",
+    "import",
     "inline",
     "int",
     "long",
+    "module",
     "namespace",
     "new",
     "not",
@@ -166,6 +174,7 @@ _CPP_KEYWORDS = {
     "public",
     "register",
     "return",
+    "requires",
     "short",
     "signed",
     "sizeof",