diff --git a/sys/Makefile.include b/sys/Makefile.include
index bcaaa8462c..f6add34d89 100644
--- a/sys/Makefile.include
+++ b/sys/Makefile.include
@@ -43,7 +43,7 @@ ifneq (,$(filter cpp11-compat,$(USEMODULE)))
   USEMODULE_INCLUDES += $(RIOTBASE)/sys/cpp11-compat/include
   # make sure cppsupport.o is linked explicitly because __dso_handle is not
   # found if it is hidden away inside a static object.
-  export UNDEF += $(BINDIR)/cpp11-compat/cppsupport.o
+  UNDEF += $(BINDIR)/cpp11-compat/cppsupport.o
 endif
 
 ifneq (,$(filter embunit,$(USEMODULE)))