diff --git a/Cargo.lock b/Cargo.lock
index bdb822187..4d487ae70 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -5266,6 +5266,16 @@ dependencies = [
  "serde_derive",
 ]
 
+[[package]]
+name = "serde_array_query"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d89c6e82b1005b33d5b2bbc47096800e5ad6b67ef5636f9c13ad29a6935734a7"
+dependencies = [
+ "serde",
+ "serde_urlencoded",
+]
+
 [[package]]
 name = "serde_cbor"
 version = "0.11.2"
@@ -6823,6 +6833,7 @@ dependencies = [
  "lighthouse_metrics",
  "safe_arith",
  "serde",
+ "serde_array_query",
  "state_processing",
  "tokio",
  "types",
diff --git a/beacon_node/http_api/src/lib.rs b/beacon_node/http_api/src/lib.rs
index 85c464466..b0907a30c 100644
--- a/beacon_node/http_api/src/lib.rs
+++ b/beacon_node/http_api/src/lib.rs
@@ -55,7 +55,10 @@ use warp::http::StatusCode;
 use warp::sse::Event;
 use warp::Reply;
 use warp::{http::Response, Filter};
-use warp_utils::task::{blocking_json_task, blocking_task};
+use warp_utils::{
+    query::multi_key_query,
+    task::{blocking_json_task, blocking_task},
+};
 
 const API_PREFIX: &str = "eth";
 
@@ -505,12 +508,13 @@ pub fn serve<T: BeaconChainTypes>(
         .clone()
         .and(warp::path("validator_balances"))
         .and(warp::path::end())
-        .and(warp::query::<api_types::ValidatorBalancesQuery>())
+        .and(multi_key_query::<api_types::ValidatorBalancesQuery>())
         .and_then(
             |state_id: StateId,
              chain: Arc<BeaconChain<T>>,
-             query: api_types::ValidatorBalancesQuery| {
+             query_res: Result<api_types::ValidatorBalancesQuery, warp::Rejection>| {
                 blocking_json_task(move || {
+                    let query = query_res?;
                     state_id
                         .map_state(&chain, |state| {
                             Ok(state
@@ -521,7 +525,7 @@ pub fn serve<T: BeaconChainTypes>(
                                 // filter by validator id(s) if provided
                                 .filter(|(index, (validator, _))| {
                                     query.id.as_ref().map_or(true, |ids| {
-                                        ids.0.iter().any(|id| match id {
+                                        ids.iter().any(|id| match id {
                                             ValidatorId::PublicKey(pubkey) => {
                                                 &validator.pubkey == pubkey
                                             }
@@ -548,11 +552,14 @@ pub fn serve<T: BeaconChainTypes>(
     let get_beacon_state_validators = beacon_states_path
         .clone()
         .and(warp::path("validators"))
-        .and(warp::query::<api_types::ValidatorsQuery>())
         .and(warp::path::end())
+        .and(multi_key_query::<api_types::ValidatorsQuery>())
         .and_then(
-            |state_id: StateId, chain: Arc<BeaconChain<T>>, query: api_types::ValidatorsQuery| {
+            |state_id: StateId,
+             chain: Arc<BeaconChain<T>>,
+             query_res: Result<api_types::ValidatorsQuery, warp::Rejection>| {
                 blocking_json_task(move || {
+                    let query = query_res?;
                     state_id
                         .map_state(&chain, |state| {
                             let epoch = state.current_epoch();
@@ -566,7 +573,7 @@ pub fn serve<T: BeaconChainTypes>(
                                 // filter by validator id(s) if provided
                                 .filter(|(index, (validator, _))| {
                                     query.id.as_ref().map_or(true, |ids| {
-                                        ids.0.iter().any(|id| match id {
+                                        ids.iter().any(|id| match id {
                                             ValidatorId::PublicKey(pubkey) => {
                                                 &validator.pubkey == pubkey
                                             }
@@ -586,8 +593,8 @@ pub fn serve<T: BeaconChainTypes>(
 
                                     let status_matches =
                                         query.status.as_ref().map_or(true, |statuses| {
-                                            statuses.0.contains(&status)
-                                                || statuses.0.contains(&status.superstatus())
+                                            statuses.contains(&status)
+                                                || statuses.contains(&status.superstatus())
                                         });
 
                                     if status_matches {
@@ -1721,11 +1728,13 @@ pub fn serve<T: BeaconChainTypes>(
         .and(warp::path("node"))
         .and(warp::path("peers"))
         .and(warp::path::end())
-        .and(warp::query::<api_types::PeersQuery>())
+        .and(multi_key_query::<api_types::PeersQuery>())
         .and(network_globals.clone())
         .and_then(
-            |query: api_types::PeersQuery, network_globals: Arc<NetworkGlobals<T::EthSpec>>| {
+            |query_res: Result<api_types::PeersQuery, warp::Rejection>,
+             network_globals: Arc<NetworkGlobals<T::EthSpec>>| {
                 blocking_json_task(move || {
+                    let query = query_res?;
                     let mut peers: Vec<api_types::PeerData> = Vec::new();
                     network_globals
                         .peers
@@ -1755,11 +1764,11 @@ pub fn serve<T: BeaconChainTypes>(
                                 );
 
                                 let state_matches = query.state.as_ref().map_or(true, |states| {
-                                    states.0.iter().any(|state_param| *state_param == state)
+                                    states.iter().any(|state_param| *state_param == state)
                                 });
                                 let direction_matches =
                                     query.direction.as_ref().map_or(true, |directions| {
-                                        directions.0.iter().any(|dir_param| *dir_param == direction)
+                                        directions.iter().any(|dir_param| *dir_param == direction)
                                     });
 
                                 if state_matches && direction_matches {
@@ -2534,16 +2543,18 @@ pub fn serve<T: BeaconChainTypes>(
     let get_events = eth1_v1
         .and(warp::path("events"))
         .and(warp::path::end())
-        .and(warp::query::<api_types::EventQuery>())
+        .and(multi_key_query::<api_types::EventQuery>())
         .and(chain_filter)
         .and_then(
-            |topics: api_types::EventQuery, chain: Arc<BeaconChain<T>>| {
+            |topics_res: Result<api_types::EventQuery, warp::Rejection>,
+             chain: Arc<BeaconChain<T>>| {
                 blocking_task(move || {
+                    let topics = topics_res?;
                     // for each topic subscribed spawn a new subscription
-                    let mut receivers = Vec::with_capacity(topics.topics.0.len());
+                    let mut receivers = Vec::with_capacity(topics.topics.len());
 
                     if let Some(event_handler) = chain.event_handler.as_ref() {
-                        for topic in topics.topics.0.clone() {
+                        for topic in topics.topics {
                             let receiver = match topic {
                                 api_types::EventTopic::Head => event_handler.subscribe_head(),
                                 api_types::EventTopic::Block => event_handler.subscribe_block(),
@@ -2606,8 +2617,8 @@ pub fn serve<T: BeaconChainTypes>(
                 .or(get_beacon_state_fork.boxed())
                 .or(get_beacon_state_finality_checkpoints.boxed())
                 .or(get_beacon_state_validator_balances.boxed())
-                .or(get_beacon_state_validators.boxed())
                 .or(get_beacon_state_validators_id.boxed())
+                .or(get_beacon_state_validators.boxed())
                 .or(get_beacon_state_committees.boxed())
                 .or(get_beacon_state_sync_committees.boxed())
                 .or(get_beacon_headers.boxed())
diff --git a/common/eth2/src/types.rs b/common/eth2/src/types.rs
index be65dd877..169a8de59 100644
--- a/common/eth2/src/types.rs
+++ b/common/eth2/src/types.rs
@@ -428,10 +428,13 @@ pub struct AttestationPoolQuery {
     pub committee_index: Option<u64>,
 }
 
-#[derive(Deserialize)]
+#[derive(Debug, Deserialize)]
+#[serde(deny_unknown_fields)]
 pub struct ValidatorsQuery {
-    pub id: Option<QueryVec<ValidatorId>>,
-    pub status: Option<QueryVec<ValidatorStatus>>,
+    #[serde(default, deserialize_with = "option_query_vec")]
+    pub id: Option<Vec<ValidatorId>>,
+    #[serde(default, deserialize_with = "option_query_vec")]
+    pub status: Option<Vec<ValidatorStatus>>,
 }
 
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
@@ -520,27 +523,68 @@ pub struct SyncingData {
 
 #[derive(Clone, PartialEq, Debug, Deserialize)]
 #[serde(try_from = "String", bound = "T: FromStr")]
-pub struct QueryVec<T: FromStr>(pub Vec<T>);
+pub struct QueryVec<T: FromStr> {
+    values: Vec<T>,
+}
+
+fn query_vec<'de, D, T>(deserializer: D) -> Result<Vec<T>, D::Error>
+where
+    D: serde::Deserializer<'de>,
+    T: FromStr,
+{
+    let vec: Vec<QueryVec<T>> = Deserialize::deserialize(deserializer)?;
+    Ok(Vec::from(QueryVec::from(vec)))
+}
+
+fn option_query_vec<'de, D, T>(deserializer: D) -> Result<Option<Vec<T>>, D::Error>
+where
+    D: serde::Deserializer<'de>,
+    T: FromStr,
+{
+    let vec: Vec<QueryVec<T>> = Deserialize::deserialize(deserializer)?;
+    if vec.is_empty() {
+        return Ok(None);
+    }
+
+    Ok(Some(Vec::from(QueryVec::from(vec))))
+}
+
+impl<T: FromStr> From<Vec<QueryVec<T>>> for QueryVec<T> {
+    fn from(vecs: Vec<QueryVec<T>>) -> Self {
+        Self {
+            values: vecs.into_iter().flat_map(|qv| qv.values).collect(),
+        }
+    }
+}
 
 impl<T: FromStr> TryFrom<String> for QueryVec<T> {
     type Error = String;
 
     fn try_from(string: String) -> Result<Self, Self::Error> {
         if string.is_empty() {
-            return Ok(Self(vec![]));
+            return Ok(Self { values: vec![] });
         }
 
-        string
-            .split(',')
-            .map(|s| s.parse().map_err(|_| "unable to parse".to_string()))
-            .collect::<Result<Vec<T>, String>>()
-            .map(Self)
+        Ok(Self {
+            values: string
+                .split(',')
+                .map(|s| s.parse().map_err(|_| "unable to parse query".to_string()))
+                .collect::<Result<Vec<T>, String>>()?,
+        })
+    }
+}
+
+impl<T: FromStr> From<QueryVec<T>> for Vec<T> {
+    fn from(vec: QueryVec<T>) -> Vec<T> {
+        vec.values
     }
 }
 
 #[derive(Clone, Deserialize)]
+#[serde(deny_unknown_fields)]
 pub struct ValidatorBalancesQuery {
-    pub id: Option<QueryVec<ValidatorId>>,
+    #[serde(default, deserialize_with = "option_query_vec")]
+    pub id: Option<Vec<ValidatorId>>,
 }
 
 #[derive(Clone, Serialize, Deserialize)]
@@ -602,9 +646,12 @@ pub struct BeaconCommitteeSubscription {
 }
 
 #[derive(Deserialize)]
+#[serde(deny_unknown_fields)]
 pub struct PeersQuery {
-    pub state: Option<QueryVec<PeerState>>,
-    pub direction: Option<QueryVec<PeerDirection>>,
+    #[serde(default, deserialize_with = "option_query_vec")]
+    pub state: Option<Vec<PeerState>>,
+    #[serde(default, deserialize_with = "option_query_vec")]
+    pub direction: Option<Vec<PeerDirection>>,
 }
 
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
@@ -858,8 +905,10 @@ impl<T: EthSpec> EventKind<T> {
 }
 
 #[derive(Clone, Deserialize)]
+#[serde(deny_unknown_fields)]
 pub struct EventQuery {
-    pub topics: QueryVec<EventTopic>,
+    #[serde(deserialize_with = "query_vec")]
+    pub topics: Vec<EventTopic>,
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Deserialize)]
@@ -961,7 +1010,9 @@ mod tests {
     fn query_vec() {
         assert_eq!(
             QueryVec::try_from("0,1,2".to_string()).unwrap(),
-            QueryVec(vec![0_u64, 1, 2])
+            QueryVec {
+                values: vec![0_u64, 1, 2]
+            }
         );
     }
 }
diff --git a/common/warp_utils/Cargo.toml b/common/warp_utils/Cargo.toml
index f99d7773b..09b6f125f 100644
--- a/common/warp_utils/Cargo.toml
+++ b/common/warp_utils/Cargo.toml
@@ -18,3 +18,4 @@ tokio = { version = "1.14.0", features = ["sync"] }
 headers = "0.3.2"
 lighthouse_metrics = { path = "../lighthouse_metrics" }
 lazy_static = "1.4.0"
+serde_array_query = "0.1.0"
diff --git a/common/warp_utils/src/lib.rs b/common/warp_utils/src/lib.rs
index 5f37dde87..346361b18 100644
--- a/common/warp_utils/src/lib.rs
+++ b/common/warp_utils/src/lib.rs
@@ -3,5 +3,6 @@
 
 pub mod cors;
 pub mod metrics;
+pub mod query;
 pub mod reject;
 pub mod task;
diff --git a/common/warp_utils/src/query.rs b/common/warp_utils/src/query.rs
new file mode 100644
index 000000000..c5ed5c5f1
--- /dev/null
+++ b/common/warp_utils/src/query.rs
@@ -0,0 +1,22 @@
+use crate::reject::custom_bad_request;
+use serde::Deserialize;
+use warp::Filter;
+
+// Custom query filter using `serde_array_query`.
+// This allows duplicate keys inside query strings.
+pub fn multi_key_query<'de, T: Deserialize<'de>>(
+) -> impl warp::Filter<Extract = (Result<T, warp::Rejection>,), Error = std::convert::Infallible> + Copy
+{
+    raw_query().then(|query_str: String| async move {
+        serde_array_query::from_str(&query_str).map_err(|e| custom_bad_request(e.to_string()))
+    })
+}
+
+// This ensures that empty query strings are still accepted.
+// This is because warp::filters::query::raw() does not allow empty query strings
+// but warp::query::<T>() does.
+fn raw_query() -> impl Filter<Extract = (String,), Error = std::convert::Infallible> + Copy {
+    warp::filters::query::raw()
+        .or(warp::any().map(String::default))
+        .unify()
+}