diff --git a/routers/repo/http.go b/routers/repo/http.go
index a9a5cedc207..c0bf830969e 100644
--- a/routers/repo/http.go
+++ b/routers/repo/http.go
@@ -427,7 +427,7 @@ func serviceRPC(h serviceHandler, service string) {
 	cmd.Stdin = reqBody
 	cmd.Stderr = &stderr
 	if err := cmd.Run(); err != nil {
-		log.Error("Fail to serve RPC(%s): %v - %v", service, err, stderr)
+		log.Error("Fail to serve RPC(%s): %v - %s", service, err, stderr.String())
 		return
 	}
 }