diff --git a/meson.build b/meson.build
index 0071e3d21c..05c403e51a 100644
--- a/meson.build
+++ b/meson.build
@@ -330,6 +330,7 @@ warning_flags = [
   '-Wno-multichar',
   '-Wvla',
   '-Wpointer-arith',
+  '-Wundef',
 ]
 
 warning_c_flags = [