diff --git a/libraries/GCS_MAVLink/GCS.h b/libraries/GCS_MAVLink/GCS.h
index 4cb5171253..bb20e7737c 100644
--- a/libraries/GCS_MAVLink/GCS.h
+++ b/libraries/GCS_MAVLink/GCS.h
@@ -51,7 +51,7 @@ public:
     void        init(AP_HAL::UARTDriver *port, mavlink_channel_t mav_chan);
     void        setup_uart(uint8_t instance);
     void        send_message(enum ap_message id);
-    void        send_text(MAV_SEVERITY severity, const char *fmt, ...) const;
+    void        send_text(MAV_SEVERITY severity, const char *fmt, ...) const FMT_PRINTF(3, 4);
     void        send_textv(MAV_SEVERITY severity, const char *fmt, va_list arg_list) const;
     void        queued_param_send();
     void        queued_mission_request_send();
@@ -696,7 +696,7 @@ public:
 
     void send_to_active_channels(uint32_t msgid, const char *pkt);
 
-    void send_text(MAV_SEVERITY severity, const char *fmt, ...);
+    void send_text(MAV_SEVERITY severity, const char *fmt, ...) FMT_PRINTF(3, 4);
     void send_textv(MAV_SEVERITY severity, const char *fmt, va_list arg_list);
     virtual void send_statustext(MAV_SEVERITY severity, uint8_t dest_bitmask, const char *text);
     void service_statustext(void);
diff --git a/libraries/GCS_MAVLink/GCS_Common.cpp b/libraries/GCS_MAVLink/GCS_Common.cpp
index f21ee40db0..6b42793b02 100644
--- a/libraries/GCS_MAVLink/GCS_Common.cpp
+++ b/libraries/GCS_MAVLink/GCS_Common.cpp
@@ -3141,7 +3141,7 @@ void GCS_MAVLINK::send_banner()
     // mark the firmware version in the tlog
     const AP_FWVersion &fwver = AP::fwversion();
 
-    send_text(MAV_SEVERITY_INFO, fwver.fw_string);
+    send_text(MAV_SEVERITY_INFO, "%s", fwver.fw_string);
 
     if (fwver.middleware_name && fwver.os_name) {
         send_text(MAV_SEVERITY_INFO, "%s: %s %s: %s",
@@ -3155,7 +3155,7 @@ void GCS_MAVLINK::send_banner()
     // send system ID if we can
     char sysid[40];
     if (hal.util->get_system_id(sysid)) {
-        send_text(MAV_SEVERITY_INFO, sysid);
+        send_text(MAV_SEVERITY_INFO, "%s", sysid);
     }
 }