diff --git a/src/mcp/client/stdio.py b/src/mcp/client/stdio.py
index 3e03eef9ef..b19cbd0d98 100644
--- a/src/mcp/client/stdio.py
+++ b/src/mcp/client/stdio.py
@@ -45,6 +45,7 @@
         "LOCALAPPDATA",
         "PATH",
         "PATHEXT",
+        "PROGRAMDATA",
         "PROCESSOR_ARCHITECTURE",
         "SYSTEMDRIVE",
         "SYSTEMROOT",