diff --git a/source/build/src/sdlayer.cpp b/source/build/src/sdlayer.cpp
index 7f99a0754..d9593033e 100644
--- a/source/build/src/sdlayer.cpp
+++ b/source/build/src/sdlayer.cpp
@@ -438,7 +438,9 @@ int main(int argc, char *argv[])
     if ((argp = Bgetenv("BUILD_NOFOG")) != NULL)
         nofog = Batol(argp);
 
-    putenv("__GL_THREADED_OPTIMIZATIONS=1");
+#ifndef _WIN32
+    setenv("__GL_THREADED_OPTIMIZATIONS", "1", 0);
+#endif
 #endif
 
     buildkeytranslationtable();