diff --git a/Makefile b/Makefile
index a1c6307..4e3d65b 100644
--- a/Makefile
+++ b/Makefile
@@ -233,7 +233,7 @@
 # Build the documentation
 #
 
-DOXY_INPUT = \
+DOXY_INPUT ?= \
 	README.md \
 	vppinfra \
 	svm \
diff --git a/doxygen/doxygen.cfg b/doxygen/doxygen.cfg
index cc10a9d..85c6829 100644
--- a/doxygen/doxygen.cfg
+++ b/doxygen/doxygen.cfg
@@ -2022,7 +2022,7 @@
 # preprocessor.
 # This tag requires that the tag SEARCH_INCLUDES is set to YES.
 
-INCLUDE_PATH           =
+INCLUDE_PATH           = $(INPUT)
 
 # You can use the INCLUDE_FILE_PATTERNS tag to specify one or more wildcard
 # patterns (like *.h and *.hpp) to filter out the header-files in the