diff --git a/crates/relayer/src/config.rs b/crates/relayer/src/config.rs
index 10721a7348..98fe08b687 100644
--- a/crates/relayer/src/config.rs
+++ b/crates/relayer/src/config.rs
@@ -618,18 +618,13 @@ pub enum EventSourceMode {
     },
 }
 
-// NOTE:
-// To work around a limitation of serde, which does not allow
+// NOTE: To work around a limitation of serde, which does not allow
 // to specify a default variant if not tag is present,
-// every underlying chain config MUST have a field `r#type` of
-// type `monotstate::MustBe!("VariantName")`.
-//
-// For chains other than CosmosSdk, this field MUST NOT be annotated
-// with `#[serde(default)]`.
-//
-// See https://github.com/serde-rs/serde/issues/2231
-#[derive(Clone, Debug, PartialEq, Deserialize, Serialize)]
-#[serde(untagged)]
+// every underlying chain config struct  MUST have a field `r#type` with
+// type `monotstate::MustBe!("VariantName")`, eg. the `CosmosSdkConfig`
+// struct has a field `r#type: MustBe!("CosmosSdk")`.
+#[derive(Clone, Debug, PartialEq, Serialize)]
+#[serde(tag = "type")]
 pub enum ChainConfig {
     CosmosSdk(CosmosSdkConfig),
 }
@@ -704,6 +699,34 @@ impl ChainConfig {
     }
 }
 
+impl<'de> Deserialize<'de> for ChainConfig {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        let value = toml::Value::deserialize(deserializer)?;
+
+        let type_value = value
+            .get("type")
+            .cloned()
+            .unwrap_or_else(|| toml::Value::String("CosmosSdk".to_string()));
+
+        let type_str = type_value
+            .as_str()
+            .ok_or_else(|| serde::de::Error::custom("invalid chain type, must be a string"))?;
+
+        match type_str {
+            "CosmosSdk" => CosmosSdkConfig::deserialize(value)
+                .map(Self::CosmosSdk)
+                .map_err(|e| serde::de::Error::custom(format!("invalid CosmosSdk config: {e}"))),
+
+            chain_type => Err(serde::de::Error::custom(format!(
+                "unknown chain type: {chain_type}",
+            ))),
+        }
+    }
+}
+
 /// Attempt to load and parse the TOML config file as a `Config`.
 pub fn load(path: impl AsRef<Path>) -> Result<Config, Error> {
     let config_toml = std::fs::read_to_string(&path).map_err(Error::io)?;