diff --git a/configure b/configure
index df6ffa2d18..2b141fbf92 100755
--- a/configure
+++ b/configure
@@ -4802,6 +4802,7 @@ case $target_os in
         objformat="win32"
         enable dos_paths
         enabled shared && ! enabled small && check_cmd $windres --version && enable gnu_windres
+        add_cppflags -D_POSIX_C_SOURCE=200112 -D_XOPEN_SOURCE=600
         ;;
     *-dos|freedos|opendos)
         network_extralibs="-lsocket"