diff --git a/zebra-chain/src/transaction/sighash.rs b/zebra-chain/src/transaction/sighash.rs
index 5395c284..4076c4a6 100644
--- a/zebra-chain/src/transaction/sighash.rs
+++ b/zebra-chain/src/transaction/sighash.rs
@@ -68,7 +68,7 @@ impl<'a> SigHasher<'a> {
         use NetworkUpgrade::*;
 
         match self.network_upgrade {
-            Genesis | BeforeOverwinter => unreachable!(ZIP143_EXPLANATION),
+            Genesis | BeforeOverwinter => unreachable!("{}", ZIP143_EXPLANATION),
             Overwinter | Sapling | Blossom | Heartwood | Canopy | Nu5 => {
                 self.hash_sighash_librustzcash()
             }