diff --git a/libraries/AP_HAL_ChibiOS/hwdef/common/hrt.h b/libraries/AP_HAL_ChibiOS/hwdef/common/hrt.h
index 302c685241..055ec1d5b3 100644
--- a/libraries/AP_HAL_ChibiOS/hwdef/common/hrt.h
+++ b/libraries/AP_HAL_ChibiOS/hwdef/common/hrt.h
@@ -4,8 +4,8 @@
 #ifdef __cplusplus
 extern "C" {
 #endif
-void hrt_init();
-uint64_t hrt_micros();
-#if __cplusplus
+void hrt_init(void);
+uint64_t hrt_micros(void);
+#ifdef __cplusplus
 }
 #endif
diff --git a/libraries/AP_HAL_ChibiOS/hwdef/common/posix.h b/libraries/AP_HAL_ChibiOS/hwdef/common/posix.h
index 42239823be..71a988fad5 100644
--- a/libraries/AP_HAL_ChibiOS/hwdef/common/posix.h
+++ b/libraries/AP_HAL_ChibiOS/hwdef/common/posix.h
@@ -379,7 +379,7 @@ int posix_fopen_modes_to_open ( const char *mode );
 
 int fprintf(FILE *fp, const char *format, ...);
 
-#if __cplusplus
+#ifdef __cplusplus
 }
 #endif
 
diff --git a/libraries/AP_HAL_ChibiOS/hwdef/common/ppm.h b/libraries/AP_HAL_ChibiOS/hwdef/common/ppm.h
index a0345cc544..456eb052af 100644
--- a/libraries/AP_HAL_ChibiOS/hwdef/common/ppm.h
+++ b/libraries/AP_HAL_ChibiOS/hwdef/common/ppm.h
@@ -23,6 +23,6 @@ uint16_t ppm_read(uint8_t chan);
 
 uint8_t ppm_read_bulk(uint16_t periods[], uint8_t len);
 bool ppm_available();
-#if __cplusplus
+#ifdef __cplusplus
 }
 #endif