diff --git a/lib-src/ntlib.c b/lib-src/ntlib.c
index 678d969c04f..110a8ccb002 100644
--- a/lib-src/ntlib.c
+++ b/lib-src/ntlib.c
@@ -58,7 +58,7 @@ getppid(void)
   char *ppid;
   DWORD result;
 
-  ppid = getenv ("__PARENT_PROCESS_ID");
+  ppid = getenv ("EM_PARENT_PROCESS_ID");
   if (!ppid) 
     {
       printf("no pid.\n");