diff --git a/serial_link.mk b/serial_link.mk
index 434966a22..f0cd60b04 100644
--- a/serial_link.mk
+++ b/serial_link.mk
@@ -20,6 +20,6 @@
 # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 # SOFTWARE.
 
-INC += $(SERIAL_DIR)
+UINCDIR += $(SERIAL_DIR)
 SRC += $(wildcard $(SERIAL_DIR)/serial_link/protocol/*.c)
 SRC += $(wildcard $(SERIAL_DIR)/serial_link/system/*.c)
\ No newline at end of file