diff --git a/crates/chainspec/src/spec.rs b/crates/chainspec/src/spec.rs
index 3816175c46cb8..80064acdf58d1 100644
--- a/crates/chainspec/src/spec.rs
+++ b/crates/chainspec/src/spec.rs
@@ -644,6 +644,7 @@ impl From<Genesis> for ChainSpec {
     fn from(genesis: Genesis) -> Self {
         // Block-based hardforks
         let hardfork_opts = [
+            (EthereumHardfork::Frontier.boxed(), Some(0)),
             (EthereumHardfork::Homestead.boxed(), genesis.config.homestead_block),
             (EthereumHardfork::Dao.boxed(), genesis.config.dao_fork_block),
             (EthereumHardfork::Tangerine.boxed(), genesis.config.eip150_block),
diff --git a/crates/optimism/chainspec/src/lib.rs b/crates/optimism/chainspec/src/lib.rs
index 98a019e85844f..deace12ec4080 100644
--- a/crates/optimism/chainspec/src/lib.rs
+++ b/crates/optimism/chainspec/src/lib.rs
@@ -346,6 +346,7 @@ impl From<Genesis> for OpChainSpec {
 
         // Block-based hardforks
         let hardfork_opts = [
+            (EthereumHardfork::Frontier.boxed(), Some(0)),
             (EthereumHardfork::Homestead.boxed(), genesis.config.homestead_block),
             (EthereumHardfork::Tangerine.boxed(), genesis.config.eip150_block),
             (EthereumHardfork::SpuriousDragon.boxed(), genesis.config.eip155_block),