diff --git a/middleware/gzip/gzip.go b/middleware/gzip/gzip.go
index 147d739f..39a92266 100644
--- a/middleware/gzip/gzip.go
+++ b/middleware/gzip/gzip.go
@@ -113,7 +113,7 @@ type gzipResponseWriter struct {
 func (w gzipResponseWriter) WriteHeader(code int) {
 	w.Header().Del("Content-Length")
 	w.Header().Set("Content-Encoding", "gzip")
-	w.Header().Set("Vary", "Accept-Encoding")
+	w.Header().Add("Vary", "Accept-Encoding")
 	w.ResponseWriter.WriteHeader(code)
 }