diff --git a/service/src/main/proto/org/signal/chat/messages.proto b/service/src/main/proto/org/signal/chat/messages.proto
index 2eb7bd08a..7d3d2c1d4 100644
--- a/service/src/main/proto/org/signal/chat/messages.proto
+++ b/service/src/main/proto/org/signal/chat/messages.proto
@@ -361,7 +361,7 @@ message ChallengeRequired {
 
   // An opaque token identifying this challenge request. Clients must generally
   // submit this token when submitting a challenge response.
-  bytes token = 1;
+  string token = 1;
 
   // A list of challenge types callers may choose to complete to resolve the
   // challenge requirement. May be empty, in which case callers cannot resolve