diff --git a/samples/net/coap_observe_client/src/Makefile b/samples/net/coap_observe_client/src/Makefile
index a5683810a5c..450b9eefbb9 100644
--- a/samples/net/coap_observe_client/src/Makefile
+++ b/samples/net/coap_observe_client/src/Makefile
@@ -1,4 +1,5 @@
 ccflags-y += ${PROJECTINCLUDE}
+ccflags-y +=-I${srctree}/net/ip
 ccflags-y +=-I${srctree}/net/ip/contiki
 ccflags-y +=-I${srctree}/net/ip/contiki/os/lib
 ccflags-y +=-I${srctree}/net/ip/contiki/os/sys