diff --git a/Lib/sysconfig.py b/Lib/sysconfig.py
index 8035d2e273e33c..f359835c636b8e 100644
--- a/Lib/sysconfig.py
+++ b/Lib/sysconfig.py
@@ -542,7 +542,7 @@ def _generate_posix_vars():
 
         for key in keys_to_replace:
             value = build_time_vars[key]
-            build_time_vars[key] = value.replace(prefix, sys.prefix)
+            build_time_vars[key] = value.replace(prefix, sys.base_prefix)
     """
 
     with open(destfile, 'w', encoding='utf8') as f: