diff --git a/main.go b/main.go
index d8fc48753..460e434ea 100644
--- a/main.go
+++ b/main.go
@@ -550,7 +550,12 @@ func (opts *Options) initUpstreams(
 	}
 
 	if opts.UpstreamMode != "" {
-		return config.UpstreamMode.UnmarshalText([]byte(opts.UpstreamMode))
+		err = config.UpstreamMode.UnmarshalText([]byte(opts.UpstreamMode))
+		if err != nil {
+			return fmt.Errorf("parsing upstream mode: %w", err)
+		}
+
+		return nil
 	}
 
 	config.UpstreamMode = proxy.UpstreamModeLoadBalance