diff --git a/src/betterproto/casing.py b/src/betterproto/casing.py
index cd3c34472..ed8299135 100644
--- a/src/betterproto/casing.py
+++ b/src/betterproto/casing.py
@@ -133,6 +133,16 @@ def lowercase_first(value: str) -> str:
     return value[0:1].lower() + value[1:]
 
 
+def is_reserved_name(value: str) -> bool:
+    if keyword.iskeyword(value):
+        return True
+
+    if value in ("bytes", "str"):
+        return True
+
+    return False
+
+
 def sanitize_name(value: str) -> str:
     # https://www.python.org/dev/peps/pep-0008/#descriptive-naming-styles
-    return f"{value}_" if keyword.iskeyword(value) else value
+    return f"{value}_" if is_reserved_name(value) else value
diff --git a/tests/inputs/config.py b/tests/inputs/config.py
index 9b7b288d3..d72fc24e7 100644
--- a/tests/inputs/config.py
+++ b/tests/inputs/config.py
@@ -3,7 +3,6 @@
 xfail = {
     "oneof_enum",  # 63
     "namespace_keywords",  # 70
-    "namespace_builtin_types",  # 53
     "googletypes_struct",  # 9
     "googletypes_value",  # 9
     "import_capitalized_package",