diff --git a/cardano-api/src/Cardano/Api/Block.hs b/cardano-api/src/Cardano/Api/Block.hs
index db9b377146d..9cee4d9af87 100644
--- a/cardano-api/src/Cardano/Api/Block.hs
+++ b/cardano-api/src/Cardano/Api/Block.hs
@@ -191,7 +191,7 @@ obtainConsensusShelleyBasedEra ShelleyBasedEraAlonzo  f = f
 -- different block types for all the eras. It is used in the ChainSync protocol.
 --
 data BlockInMode mode where
-     BlockInMode :: Block era -> EraInMode era mode -> BlockInMode mode
+     BlockInMode :: IsCardanoEra era => Block era -> EraInMode era mode -> BlockInMode mode
 
 deriving instance Show (BlockInMode mode)