diff --git a/dist/tools/buildsystem_sanity_check/check.sh b/dist/tools/buildsystem_sanity_check/check.sh
index e2a3d613b7..c5eb0a9141 100755
--- a/dist/tools/buildsystem_sanity_check/check.sh
+++ b/dist/tools/buildsystem_sanity_check/check.sh
@@ -85,6 +85,7 @@ UNEXPORTED_VARIABLES+=('USEMODULE_INCLUDES')
 EXPORTED_VARIABLES_ONLY_IN_VARS=()
 EXPORTED_VARIABLES_ONLY_IN_VARS+=('CPU_ARCH')
 EXPORTED_VARIABLES_ONLY_IN_VARS+=('CPU_FAM')
+EXPORTED_VARIABLES_ONLY_IN_VARS+=('UNDEF')
 EXPORTED_VARIABLES_ONLY_IN_VARS+=('USEMODULE')
 EXPORTED_VARIABLES_ONLY_IN_VARS+=('TOOLCHAIN')
 EXPORTED_VARIABLES_ONLY_IN_VARS+=('WERROR')