From 9804d03e1f54e94309bb611d87cb783afcbc9ed9 Mon Sep 17 00:00:00 2001
From: "jan.nijtmans" <nijtmans@users.sourceforge.net>
Date: Fri, 16 Jul 2021 15:52:34 +0000
Subject: Proposed fix for [592a25a505]: Tcl_PutEnv() crashes on Windows

---
 generic/tclEnv.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/generic/tclEnv.c b/generic/tclEnv.c
index e4246a1..2788c7e 100644
--- a/generic/tclEnv.c
+++ b/generic/tclEnv.c
@@ -420,6 +420,16 @@ Tcl_PutEnv(
 
     if ((value != NULL) && (value != name)) {
 	value[0] = '\0';
+#if defined(_WIN32)
+	if (tenviron == NULL) {
+	    /*
+	     * When we are started from main(), the _wenviron array could
+	     * be NULL and will be initialized by the first _wgetenv() call.
+	     */
+
+	(void) _wgetenv(L"WINDIR");
+	}
+#endif
 	TclSetEnv(name, value+1);
     }
     TclEnvEpoch++;
-- 
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