diff --git a/image.in/functions.mk b/image.in/functions.mk
index 79b0a162..7c247f23 100644
--- a/image.in/functions.mk
+++ b/image.in/functions.mk
@@ -1,6 +1,9 @@
 ifneq (clean,$(MAKECMDGOALS))
 ifneq (distclean,$(MAKECMDGOALS))
 
+ifndef INCLUDED_FUNCTIONS_MK
+INCLUDED_FUNCTIONS_MK = 1
+
 # globals
 PKGDIR ?= $(GLOBAL_BUILDDIR)/pkg
 
@@ -49,3 +52,4 @@ branding = $(and $(1),^branding-$(BRANDING)-($(call list2re,$(1)))$$)
 
 endif
 endif
+endif