diff --git a/stdlib/3/sys.pyi b/stdlib/3/sys.pyi
index 14a9721fbffd..471ba5ea1874 100644
--- a/stdlib/3/sys.pyi
+++ b/stdlib/3/sys.pyi
@@ -46,6 +46,8 @@ path_hooks: List[Any]  # TODO precise type; function, path to finder
 path_importer_cache: Dict[str, Any]  # TODO precise type
 platform: str
 prefix: str
+if sys.version_info >= (3, 8):
+    pycache_prefix: Optional[str]
 ps1: str
 ps2: str
 stdin: TextIO