diff --git a/stdlib/3/subprocess.pyi b/stdlib/3/subprocess.pyi
index 8bb75ab23863..41ddb9a616e4 100644
--- a/stdlib/3/subprocess.pyi
+++ b/stdlib/3/subprocess.pyi
@@ -350,4 +350,6 @@ class Popen:
 def getstatusoutput(cmd: _TXT) -> Tuple[int, str]: ...
 def getoutput(cmd: _TXT) -> str: ...
 
+def list2cmdline(seq: Sequence[str]) -> str: ...  # undocumented
+
 # Windows-only: STARTUPINFO etc.