diff --git a/libraries/AP_GPS/AP_GPS_GSOF.h b/libraries/AP_GPS/AP_GPS_GSOF.h
index d1f7589818..946242736d 100644
--- a/libraries/AP_GPS/AP_GPS_GSOF.h
+++ b/libraries/AP_GPS/AP_GPS_GSOF.h
@@ -82,6 +82,6 @@ private:
 
     uint32_t gsofmsg_time = 0;
     uint8_t gsofmsgreq_index = 0;
-    uint8_t gsofmsgreq[5] = {1,2,8,9,12};
+    const uint8_t gsofmsgreq[5] = {1,2,8,9,12};
 };
 #endif