diff --git a/cardano-cli/src/Cardano/CLI/Types/Errors/TxValidationError.hs b/cardano-cli/src/Cardano/CLI/Types/Errors/TxValidationError.hs
index d414f9c22e..5342b270bc 100644
--- a/cardano-cli/src/Cardano/CLI/Types/Errors/TxValidationError.hs
+++ b/cardano-cli/src/Cardano/CLI/Types/Errors/TxValidationError.hs
@@ -353,11 +353,13 @@ convToTxProposalProcedures
   :: Ledger.EraPParams (ShelleyLedgerEra era)
   => [(Proposal era, Maybe (ScriptWitness WitCtxStake era))]
   -> TxProposalProcedures BuildTx era
-convToTxProposalProcedures proposalProcedures =
+convToTxProposalProcedures proposalProcedures = do
    -- TODO: Ledger does not export snoc so we can't fold here.
    let proposals = OSet.fromFoldable $ map (unProposal . fst) proposalProcedures
-       sWitMap = BuildTxWith $ foldl sWitMapFolder Map.empty proposalProcedures
-   in TxProposalProcedures proposals sWitMap
+   case Map.size sWitMap of
+     0 -> error "convToTxProposalProcedures: No script witness found for proposal."
+     _ -> TxProposalProcedures proposals $ BuildTxWith sWitMap
   where
+   sWitMap = foldl sWitMapFolder Map.empty proposalProcedures
    sWitMapFolder sWitMapAccum nextSWit = sWitMapAccum `Map.union` uncurry proposingScriptWitnessSingleton nextSWit