diff --git a/Makefile.include b/Makefile.include
index 4933d204e..023bb711b 100644
--- a/Makefile.include
+++ b/Makefile.include
@@ -14,6 +14,10 @@ ifeq ($(TARGET),)
   endif
 endif
 
+ifeq ($(UIP_CONF_IPV6),1)
+  CFLAGS += -DUIP_CONF_IPV6=1
+endif
+
 ifeq ($(DEFINES),)
   -include Makefile.$(TARGET).defines
   ifneq ($(DEFINES),)