diff --git a/conf/Makefile.avr b/conf/Makefile.avr
index 52e52f88a8..979e133746 100644
--- a/conf/Makefile.avr
+++ b/conf/Makefile.avr
@@ -65,7 +65,7 @@ Q=@
 
 
 CFLAGS		=							\
-	-Werror -W -Wall -Wundef \
+	-W -Wall -Wundef \
 	$(ATMEL_INCLUDES)					  	\
 	$(INCLUDES)					  	\
 	-Wstrict-prototypes						\
diff --git a/conf/Makefile.sim b/conf/Makefile.sim
index a5d511b729..65f3ff5adf 100644
--- a/conf/Makefile.sim
+++ b/conf/Makefile.sim
@@ -45,7 +45,7 @@ Q=@
 
 
 CFLAGS		=							\
-	-W -Wall -Werror \
+	-W -Wall \
 	$(INCLUDES)					  	\
 	-Wstrict-prototypes						\
 	$($(TARGET).CFLAGS)					\
diff --git a/conf/airframes/twinstar2.xml b/conf/airframes/twinstar2.xml
index 7110c72bb1..79cc4a7e0f 100644
--- a/conf/airframes/twinstar2.xml
+++ b/conf/airframes/twinstar2.xml
@@ -123,6 +123,9 @@ ap.CFLAGS += -DMOBILE_CAM -DDATALINK
 ap.EXTRA_SRCS += traffic_info.c datalink.c
 ap.CFLAGS += -DUSE_UART0 -DHITL
 
+-DDOWNLINK -DDOWNLINK_TRANSPORT=PprzTransport -DDOWNLINK_AP_DEVICE=Uart0
+ap.EXTRA_SRCS += pprz_transport.c downlink.c
+
 # Config for SITL simulation
 include $(PAPARAZZI_SRC)/conf/autopilot/sitl.makefile
 sim.CFLAGS += -DDATALINK -DMOBILE_CAM
diff --git a/sw/airborne/ap_downlink.h b/sw/airborne/ap_downlink.h
index ba1039a277..51c3ec3606 100644
--- a/sw/airborne/ap_downlink.h
+++ b/sw/airborne/ap_downlink.h
@@ -35,7 +35,7 @@
 #include "messages.h"
 #include "periodic.h"
 
-#if DOWNLINK
+#if defined DOWNLINK
 #define Downlink(x) x
 #else
 #define Downlink(x) {}