diff --git a/libraries/AP_HAL_ChibiOS/system.cpp b/libraries/AP_HAL_ChibiOS/system.cpp
index 45c5ec96b0..c827cb9dc4 100644
--- a/libraries/AP_HAL_ChibiOS/system.cpp
+++ b/libraries/AP_HAL_ChibiOS/system.cpp
@@ -226,7 +226,9 @@ void panic(const char *errormsg, ...)
 
     hal.scheduler->delay_microseconds(10000);
     while (1) {
+        va_start(ap, errormsg);
         vprintf(errormsg, ap);
+        va_end(ap);
         hal.scheduler->delay(500);
     }
 #else