diff --git a/tonic/src/codec/decode.rs b/tonic/src/codec/decode.rs
index 73f3427af..dc68d7c52 100644
--- a/tonic/src/codec/decode.rs
+++ b/tonic/src/codec/decode.rs
@@ -173,11 +173,11 @@ impl<T> Streaming<T> {
                     trace!("unexpected compression flag");
                     let message = if let Direction::Response(status) = self.direction {
                         format!(
-                            "Unexpected compression flag: {}, while receiving response with status: {}",
+                            "protocol error: received message with invalid compression flag: {} (valid flags are 0 and 1) while receiving response with status: {}",
                             f, status
                         )
                     } else {
-                        format!("Unexpected compression flag: {}, while sending request", f)
+                        format!("protocol error: received message with invalid compression flag: {} (valid flags are 0 and 1), while sending request", f)
                     };
                     return Err(Status::new(Code::Internal, message));
                 }