diff --git a/beacon_node/execution_layer/src/engine_api/http.rs b/beacon_node/execution_layer/src/engine_api/http.rs
index 5dce3500b0..0445bc5c5e 100644
--- a/beacon_node/execution_layer/src/engine_api/http.rs
+++ b/beacon_node/execution_layer/src/engine_api/http.rs
@@ -503,7 +503,7 @@ mod test {
                         "gasLimit": "0x1",
                         "gasUsed": "0x2",
                         "timestamp": "0x2a",
-                        "extraData": [],
+                        "extraData": "0x",
                         "baseFeePerGas": HASH_00,
                         "blockHash": HASH_01,
                         "transactions": [],
diff --git a/consensus/ssz_types/src/serde_utils/hex_fixed_vec.rs b/consensus/ssz_types/src/serde_utils/hex_fixed_vec.rs
index 0b1b73f014..86077891bc 100644
--- a/consensus/ssz_types/src/serde_utils/hex_fixed_vec.rs
+++ b/consensus/ssz_types/src/serde_utils/hex_fixed_vec.rs
@@ -8,10 +8,7 @@ where
     S: Serializer,
     U: Unsigned,
 {
-    let mut hex_string: String = "0x".to_string();
-    hex_string.push_str(&hex::encode(&bytes[..]));
-
-    serializer.serialize_str(&hex_string)
+    serializer.serialize_str(&hex::encode(&bytes[..]))
 }
 
 pub fn deserialize<'de, D, U>(deserializer: D) -> Result<FixedVector<u8, U>, D::Error>
diff --git a/consensus/ssz_types/src/serde_utils/hex_var_list.rs b/consensus/ssz_types/src/serde_utils/hex_var_list.rs
index 3fc52951b9..e3a3a14e06 100644
--- a/consensus/ssz_types/src/serde_utils/hex_var_list.rs
+++ b/consensus/ssz_types/src/serde_utils/hex_var_list.rs
@@ -9,10 +9,7 @@ where
     S: Serializer,
     N: Unsigned,
 {
-    let mut hex_string: String = "0x".to_string();
-    hex_string.push_str(&hex::encode(&**bytes));
-
-    serializer.serialize_str(&hex_string)
+    serializer.serialize_str(&hex::encode(&**bytes))
 }
 
 pub fn deserialize<'de, D, N>(deserializer: D) -> Result<VariableList<u8, N>, D::Error>