diff --git a/vars/build.vars b/vars/build.vars
index 3840cfc..54e08de 100644
--- a/vars/build.vars
+++ b/vars/build.vars
@@ -346,7 +346,7 @@ NATIVE_RUNTIME_PREFIX="${PREFIX_NATIVE}";
 : ${PKG_PTYCON_URLS_GIT:=ptycon=${DEFAULT_GITROOT}/ptycon};
 : ${PKG_PTYCON_CFLAGS_CONFIGURE_EXTRA:=-O0};
 : ${PKG_PTYCON_INSTALL_TARGET_EXTRA:="install-app install-lib"};
-: ${PKG_U16PORTS_CFLAGS_CONFIGURE_EXTRA:=-Wno-error=missing-field-initializers};
+: ${PKG_U16PORTS_CFLAGS_CONFIGURE_EXTRA:="--sysroot=${PREFIX_NATIVE} -Wno-missing-field-initializers"};
 : ${PKG_U16PORTS_URLS_GIT:=u16ports=${DEFAULT_GITROOT}/u16ports};
 : ${PKG_U16PORTS_INSTALL_TARGET_EXTRA:=install-lib};