diff --git a/test/coap-service/unittest/makefile_defines.txt b/test/coap-service/unittest/makefile_defines.txt
index 9b6e5a0a5003..dc1f53eb308b 100755
--- a/test/coap-service/unittest/makefile_defines.txt
+++ b/test/coap-service/unittest/makefile_defines.txt
@@ -33,6 +33,7 @@ INCLUDE_DIRS =\
   ../../../../../event-loop/source/ \
   ../../../../../mbedtls/include/ \
   ../../../../../mbedtls/include/mbedtls/ \
+  ../../../../../mbedtls/crypto/include/ \
   /usr/include\
   $(CPPUTEST_HOME)/include\