diff --git a/config.project b/config.project
index f06614e..2a01ab6 100644
--- a/config.project
+++ b/config.project
@@ -42,7 +42,7 @@ mb_hosted=
 mb_freestanding=
 
 # switches
-mb_default_cflags_common="-std=c99 -D_XOPEN_SOURCE=700"
+mb_default_cflags_common="\$(_CFLAGS_std_c99) -D_XOPEN_SOURCE=700"
 mb_default_cflags_common="$mb_default_cflags_common -Ibuild"
 
 mb_default_cflags_debug=
@@ -67,5 +67,5 @@ mb_default_ldflags_last=
 mb_default_ldflags_once=
 
 # native
-mb_default_native_cflags="-std=c99 -D_XOPEN_SOURCE=700"
+mb_default_native_cflags="\$(_NATIVE_CFLAGS_std_c99) -D_XOPEN_SOURCE=700"
 mb_default_native_ldflags=