diff --git a/apps/px4io/protocol.h b/apps/px4io/protocol.h
index edc2c4bd2d..c4a63d8869 100644
--- a/apps/px4io/protocol.h
+++ b/apps/px4io/protocol.h
@@ -48,7 +48,7 @@
 
 #define PX4IO_OUTPUT_CHANNELS	8
 #define PX4IO_INPUT_CHANNELS	12
-#define PX4IO_RELAY_CHANNELS	2
+#define PX4IO_RELAY_CHANNELS	4
 
 #pragma pack(push, 1)