diff --git a/consensus/types/src/chain_spec.rs b/consensus/types/src/chain_spec.rs
index 0bd0acb96..f191eb867 100644
--- a/consensus/types/src/chain_spec.rs
+++ b/consensus/types/src/chain_spec.rs
@@ -611,9 +611,15 @@ pub struct Config {
     #[serde(default)]
     pub preset_base: String,
 
+    // TODO(merge): remove this default
+    #[serde(default = "default_terminal_total_difficulty")]
     #[serde(with = "eth2_serde_utils::quoted_u256")]
     pub terminal_total_difficulty: Uint256,
+    // TODO(merge): remove this default
+    #[serde(default = "default_terminal_block_hash")]
     pub terminal_block_hash: Hash256,
+    // TODO(merge): remove this default
+    #[serde(default = "default_terminal_block_hash_activation_epoch")]
     pub terminal_block_hash_activation_epoch: Epoch,
 
     #[serde(with = "eth2_serde_utils::quoted_u64")]
@@ -682,6 +688,20 @@ fn default_bellatrix_fork_epoch() -> Option<MaybeQuoted<Epoch>> {
     None
 }
 
+fn default_terminal_total_difficulty() -> Uint256 {
+    "115792089237316195423570985008687907853269984665640564039457584007913129638912"
+        .parse()
+        .unwrap()
+}
+
+fn default_terminal_block_hash() -> Hash256 {
+    Hash256::zero()
+}
+
+fn default_terminal_block_hash_activation_epoch() -> Epoch {
+    Epoch::new(u64::MAX)
+}
+
 impl Default for Config {
     fn default() -> Self {
         let chain_spec = MainnetEthSpec::default_spec();