diff --git a/stdlib/3/gzip.pyi b/stdlib/3/gzip.pyi
index 024413b09..6f1bf7adc 100644
--- a/stdlib/3/gzip.pyi
+++ b/stdlib/3/gzip.pyi
@@ -23,7 +23,7 @@ class GzipFile(_compression.BaseStream):
     @property
     def filename(self) -> str: ...
     @property
-    def mtime(self): ...
+    def mtime(self) -> Optional[int]: ...
     crc: int
     def write(self, data: bytes) -> int: ...
     def read(self, size: Optional[int] = ...) -> bytes: ...