diff --git a/src/verification.ml b/src/verification.ml
index 3aa186a85fd618af85a6e3538361b0d2d80580f9..707340ba8a9fb19e8e5e5cf63aa609d48ecd9399 100644
--- a/src/verification.ml
+++ b/src/verification.ml
@@ -178,6 +178,7 @@ let combine_prover_answers answers =
   List.fold_left answers ~init:Call_provers.Valid ~f:(fun acc r ->
     match (acc, r) with
     | Call_provers.Valid, r | r, Call_provers.Valid -> r
+    | Invalid, _ | _, Invalid -> Invalid
     | _ -> acc)
 
 let answer_dataset limit config env prover config_prover driver dataset task =