diff --git a/Cargo.lock b/Cargo.lock
index 59e7bda170..516d0df358 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1235,10 +1235,12 @@ dependencies = [
  "eth2",
  "ethereum_ssz",
  "lighthouse_version",
+ "mockito",
  "reqwest 0.11.27",
  "sensitive_url",
  "serde",
  "serde_json",
+ "tokio",
 ]
 
 [[package]]
diff --git a/beacon_node/builder_client/Cargo.toml b/beacon_node/builder_client/Cargo.toml
index 1920bd0ebb..9b1f86360d 100644
--- a/beacon_node/builder_client/Cargo.toml
+++ b/beacon_node/builder_client/Cargo.toml
@@ -12,3 +12,7 @@ reqwest = { workspace = true }
 sensitive_url = { workspace = true }
 serde = { workspace = true }
 serde_json = { workspace = true }
+
+[dev-dependencies]
+mockito = { workspace = true }
+tokio = { workspace = true }
diff --git a/beacon_node/builder_client/src/lib.rs b/beacon_node/builder_client/src/lib.rs
index 2c83e34755..6b993542f3 100644
--- a/beacon_node/builder_client/src/lib.rs
+++ b/beacon_node/builder_client/src/lib.rs
@@ -155,15 +155,7 @@ impl BuilderHttpClient {
             }
             ContentType::Json => {
                 self.ssz_available.store(false, Ordering::SeqCst);
-                let mut de = serde_json::Deserializer::from_slice(&response_bytes);
-                let data =
-                    T::context_deserialize(&mut de, fork_name).map_err(Error::InvalidJson)?;
-
-                Ok(ForkVersionedResponse {
-                    version: fork_name,
-                    metadata: EmptyMetadata {},
-                    data,
-                })
+                serde_json::from_slice(&response_bytes).map_err(Error::InvalidJson)
             }
         }
     }
@@ -546,6 +538,12 @@ impl BuilderHttpClient {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use eth2::types::builder_bid::{BuilderBid, BuilderBidFulu};
+    use eth2::types::test_utils::{SeedableRng, TestRandom, XorShiftRng};
+    use eth2::types::{MainnetEthSpec, Signature};
+    use mockito::{Matcher, Server, ServerGuard};
+
+    type E = MainnetEthSpec;
 
     #[test]
     fn test_headers_no_panic() {
@@ -556,4 +554,146 @@ mod tests {
         assert!(HeaderValue::from_str(JSON_ACCEPT_VALUE).is_ok());
         assert!(HeaderValue::from_str(JSON_CONTENT_TYPE_HEADER).is_ok());
     }
+
+    #[tokio::test]
+    async fn test_get_builder_header_ssz_response() {
+        // Set up mock server
+        let mut server = Server::new_async().await;
+        let mock_response_body = fulu_signed_builder_bid();
+        mock_get_header_response(
+            &mut server,
+            Some("fulu"),
+            ContentType::Ssz,
+            mock_response_body.clone(),
+        );
+
+        let builder_client = BuilderHttpClient::new(
+            SensitiveUrl::from_str(&server.url()).unwrap(),
+            None,
+            None,
+            false,
+        )
+        .unwrap();
+
+        let response = builder_client
+            .get_builder_header(
+                Slot::new(1),
+                ExecutionBlockHash::repeat_byte(1),
+                &PublicKeyBytes::empty(),
+            )
+            .await
+            .expect("should succeed in get_builder_header")
+            .expect("should have response body");
+
+        assert_eq!(response, mock_response_body);
+    }
+
+    #[tokio::test]
+    async fn test_get_builder_header_json_response() {
+        // Set up mock server
+        let mut server = Server::new_async().await;
+        let mock_response_body = fulu_signed_builder_bid();
+        mock_get_header_response(
+            &mut server,
+            None,
+            ContentType::Json,
+            mock_response_body.clone(),
+        );
+
+        let builder_client = BuilderHttpClient::new(
+            SensitiveUrl::from_str(&server.url()).unwrap(),
+            None,
+            None,
+            false,
+        )
+        .unwrap();
+
+        let response = builder_client
+            .get_builder_header(
+                Slot::new(1),
+                ExecutionBlockHash::repeat_byte(1),
+                &PublicKeyBytes::empty(),
+            )
+            .await
+            .expect("should succeed in get_builder_header")
+            .expect("should have response body");
+
+        assert_eq!(response, mock_response_body);
+    }
+
+    #[tokio::test]
+    async fn test_get_builder_header_no_version_header_fallback_json() {
+        // Set up mock server
+        let mut server = Server::new_async().await;
+        let mock_response_body = fulu_signed_builder_bid();
+        mock_get_header_response(
+            &mut server,
+            Some("fulu"),
+            ContentType::Json,
+            mock_response_body.clone(),
+        );
+
+        let builder_client = BuilderHttpClient::new(
+            SensitiveUrl::from_str(&server.url()).unwrap(),
+            None,
+            None,
+            false,
+        )
+        .unwrap();
+
+        let response = builder_client
+            .get_builder_header(
+                Slot::new(1),
+                ExecutionBlockHash::repeat_byte(1),
+                &PublicKeyBytes::empty(),
+            )
+            .await
+            .expect("should succeed in get_builder_header")
+            .expect("should have response body");
+
+        assert_eq!(response, mock_response_body);
+    }
+
+    fn mock_get_header_response(
+        server: &mut ServerGuard,
+        header_version_opt: Option<&str>,
+        content_type: ContentType,
+        response_body: ForkVersionedResponse<SignedBuilderBid<E>>,
+    ) {
+        let mut mock = server.mock(
+            "GET",
+            Matcher::Regex(r"^/eth/v1/builder/header/\d+/.+/.+$".to_string()),
+        );
+
+        if let Some(version) = header_version_opt {
+            mock = mock.with_header(CONSENSUS_VERSION_HEADER, version);
+        }
+
+        match content_type {
+            ContentType::Json => {
+                mock = mock
+                    .with_header(CONTENT_TYPE_HEADER, JSON_CONTENT_TYPE_HEADER)
+                    .with_body(serde_json::to_string(&response_body).unwrap());
+            }
+            ContentType::Ssz => {
+                mock = mock
+                    .with_header(CONTENT_TYPE_HEADER, SSZ_CONTENT_TYPE_HEADER)
+                    .with_body(response_body.data.as_ssz_bytes());
+            }
+        }
+
+        mock.with_status(200).create();
+    }
+
+    fn fulu_signed_builder_bid() -> ForkVersionedResponse<SignedBuilderBid<E>> {
+        let rng = &mut XorShiftRng::from_seed([42; 16]);
+        ForkVersionedResponse {
+            version: ForkName::Fulu,
+            metadata: EmptyMetadata {},
+            data: SignedBuilderBid {
+                message: BuilderBid::Fulu(BuilderBidFulu::random_for_test(rng)),
+                signature: Signature::empty(),
+            },
+        }
+    }
 }