diff --git a/nimble/host/src/ble_monitor.c b/nimble/host/src/ble_monitor.c
index 93a75e68c..35e619e27 100644
--- a/nimble/host/src/ble_monitor.c
+++ b/nimble/host/src/ble_monitor.c
@@ -25,6 +25,7 @@
 #error "Cannot enable monitor over UART and RTT at the same time!"
 #endif
 
+#include <stdarg.h>
 #include <stdio.h>
 #include <inttypes.h>
 #include "os/os.h"