diff --git a/client/http/http_test.go b/client/http/http_test.go
index 19115dd..2998143 100644
--- a/client/http/http_test.go
+++ b/client/http/http_test.go
@@ -139,6 +139,7 @@ func TestHTTPClient(t *testing.T) {
 		}
 
 		// write response
+		w.Header().Add("Content-Type", "application/json")
 		w.Write(b)
 	})
 	go http.Serve(l, mux)