diff --git a/nt/mingw-cfg.site b/nt/mingw-cfg.site
index a9ca20cb155..96300774871 100644
--- a/nt/mingw-cfg.site
+++ b/nt/mingw-cfg.site
@@ -158,3 +158,7 @@ gl_cv_func_copy_file_range=yes
 # We don't want to build Emacs so it depends on bcrypt.dll, since then
 # it will refuse to start on systems where that DLL is absent.
 gl_cv_lib_assume_bcrypt=no
+# Don't build the Gnulib free.c: it is not needed, since the w32
+# implementation of 'free' doesn't touch errno, and it emits a
+# compilation warning.
+gl_cv_func_free_preserves_errno=yes