diff --git a/protos/rtk/rtk.proto b/protos/rtk/rtk.proto
index a6365ea16..311bcd4a6 100644
--- a/protos/rtk/rtk.proto
+++ b/protos/rtk/rtk.proto
@@ -15,7 +15,7 @@ service RtkService {
 
 // RTCM data type
 message RtcmData {
-    string data = 1; // The data encoded as a string
+    string data = 1; // The data encoded as a base64 string
 }
 
 message SendRtcmDataRequest {