diff --git a/libraries/AP_IOMCU/AP_IOMCU.cpp b/libraries/AP_IOMCU/AP_IOMCU.cpp
index 865f4c0646..fd8015dee2 100644
--- a/libraries/AP_IOMCU/AP_IOMCU.cpp
+++ b/libraries/AP_IOMCU/AP_IOMCU.cpp
@@ -18,6 +18,7 @@
 #include <AP_RCProtocol/AP_RCProtocol.h>
 #include <AP_InternalError/AP_InternalError.h>
 #include <AP_Logger/AP_Logger.h>
+#include <ch.h>
 
 extern const AP_HAL::HAL &hal;
 
diff --git a/libraries/AP_IOMCU/AP_IOMCU.h b/libraries/AP_IOMCU/AP_IOMCU.h
index 5fe549cdb5..a4f0f962c2 100644
--- a/libraries/AP_IOMCU/AP_IOMCU.h
+++ b/libraries/AP_IOMCU/AP_IOMCU.h
@@ -9,10 +9,12 @@
 
 #if HAL_WITH_IO_MCU
 
-#include "ch.h"
 #include "iofirmware/ioprotocol.h"
 #include <AP_RCMapper/AP_RCMapper.h>
 
+typedef uint32_t eventmask_t;
+typedef struct ch_thread thread_t;
+
 class AP_IOMCU {
 public:
     AP_IOMCU(AP_HAL::UARTDriver &uart);