diff --git a/servant-server.cabal b/servant-server.cabal
index d1fefddd..8a2f13e0 100644
--- a/servant-server.cabal
+++ b/servant-server.cabal
@@ -34,7 +34,7 @@ library
     , aeson
     , attoparsec
     , bytestring
-    , either
+    , either >= 4.3
     , http-types
     , network-uri >= 2.6
     , safe