diff --git a/beacon_node/beacon_chain/src/beacon_chain.rs b/beacon_node/beacon_chain/src/beacon_chain.rs
index d5fd113a8..966e73210 100644
--- a/beacon_node/beacon_chain/src/beacon_chain.rs
+++ b/beacon_node/beacon_chain/src/beacon_chain.rs
@@ -64,6 +64,15 @@ impl BlockProcessingOutcome {
             },
         }
     }
+
+    /// Returns `true` if the block was successfully processed and can be removed from any import
+    /// queues or temporary storage.
+    pub fn sucessfully_processed(&self) -> bool {
+        match self {
+            BlockProcessingOutcome::ValidBlock(_) => true,
+            _ => false,
+        }
+    }
 }
 
 pub struct BeaconChain<T: ClientDB + Sized, U: SlotClock, F: ForkChoice> {
diff --git a/beacon_node/network/src/sync/simple_sync.rs b/beacon_node/network/src/sync/simple_sync.rs
index 7609f5750..b77a976b1 100644
--- a/beacon_node/network/src/sync/simple_sync.rs
+++ b/beacon_node/network/src/sync/simple_sync.rs
@@ -425,14 +425,15 @@ impl SimpleSync {
     }
 
     pub fn process_import_queue(&mut self, network: &mut NetworkContext) {
-        let mut blocks: Vec<(Hash256, BeaconBlock, PeerId)> = self
+        let mut blocks: Vec<(usize, BeaconBlock, PeerId)> = self
             .import_queue
             .partials
             .iter()
-            .filter_map(|(key, partial)| {
+            .enumerate()
+            .filter_map(|(i, partial)| {
                 if let Some(_) = partial.body {
                     let (block, _root) = partial.clone().complete().expect("Body must be Some");
-                    Some((*key, block, partial.sender.clone()))
+                    Some((i, block, partial.sender.clone()))
                 } else {
                     None
                 }
@@ -469,7 +470,7 @@ impl SimpleSync {
         if !keys_to_delete.is_empty() {
             info!(self.log, "Processed {} blocks", keys_to_delete.len());
             for key in keys_to_delete {
-                self.import_queue.partials.remove(&key);
+                self.import_queue.partials.remove(key);
             }
         }
     }
@@ -539,7 +540,7 @@ pub struct ImportQueue {
     /// BeaconChain
     pub chain: Arc<BeaconChain>,
     /// Partially imported blocks, keyed by the root of `BeaconBlockBody`.
-    pub partials: HashMap<Hash256, PartialBeaconBlock>,
+    pub partials: Vec<PartialBeaconBlock>,
     /// Time before a queue entry is consider state.
     pub stale_time: Duration,
     /// Logging
@@ -550,7 +551,7 @@ impl ImportQueue {
     pub fn new(chain: Arc<BeaconChain>, stale_time: Duration, log: slog::Logger) -> Self {
         Self {
             chain,
-            partials: HashMap::new(),
+            partials: vec![],
             stale_time,
             log,
         }
@@ -561,29 +562,30 @@ impl ImportQueue {
     /// An entry is stale if it has as a `inserted` time that is more than `self.stale_time` in the
     /// past.
     pub fn remove_stale(&mut self) {
-        let keys: Vec<Hash256> = self
+        let stale_indices: Vec<usize> = self
             .partials
             .iter()
-            .filter_map(|(key, partial)| {
+            .enumerate()
+            .filter_map(|(i, partial)| {
                 if partial.inserted + self.stale_time <= Instant::now() {
-                    Some(*key)
+                    Some(i)
                 } else {
                     None
                 }
             })
             .collect();
 
-        if !keys.is_empty() {
+        if !stale_indices.is_empty() {
             debug!(
                 self.log,
                 "ImportQueue removing stale entries";
-                "stale_count" => keys.len(),
+                "stale_items" => stale_indices.len(),
                 "stale_time_seconds" => self.stale_time.as_secs()
             );
         }
 
-        keys.iter().for_each(|key| {
-            self.partials.remove(&key);
+        stale_indices.iter().for_each(|&i| {
+            self.partials.remove(i);
         });
     }
 
@@ -646,29 +648,39 @@ impl ImportQueue {
     /// If the header already exists, the `inserted` time is set to `now` and not other
     /// modifications are made.
     fn insert_header(&mut self, block_root: Hash256, header: BeaconBlockHeader, sender: PeerId) {
-        self.partials
-            .entry(header.block_body_root)
-            .and_modify(|p| p.inserted = Instant::now())
-            .or_insert(PartialBeaconBlock {
+        if let Some(i) = self
+            .partials
+            .iter()
+            .position(|p| p.block_root == block_root)
+        {
+            self.partials[i].inserted = Instant::now();
+        } else {
+            self.partials.push(PartialBeaconBlock {
                 block_root,
                 header,
                 body: None,
                 inserted: Instant::now(),
                 sender,
-            });
+            })
+        }
     }
 
     /// Updates an existing partial with the `body`.
     ///
     /// If there is no header for the `body`, the body is simply discarded.
+    ///
+    /// If the body already existed, the `inserted` time is set to `now`.
     fn insert_body(&mut self, body: BeaconBlockBody, sender: PeerId) {
         let body_root = Hash256::from_slice(&body.hash_tree_root()[..]);
 
-        self.partials.entry(body_root).and_modify(|p| {
+        self.partials.iter_mut().for_each(|mut p| {
             if body_root == p.header.block_body_root {
-                p.body = Some(body);
                 p.inserted = Instant::now();
-                p.sender = sender;
+
+                if p.body.is_none() {
+                    p.body = Some(body.clone());
+                    p.sender = sender.clone();
+                }
             }
         });
     }
diff --git a/beacon_node/network/tests/tests.rs b/beacon_node/network/tests/tests.rs
index b951d7d2a..2952e5105 100644
--- a/beacon_node/network/tests/tests.rs
+++ b/beacon_node/network/tests/tests.rs
@@ -511,7 +511,10 @@ fn sync_two_nodes() {
 
     // Node A builds out a longer, better chain.
     for _ in 0..blocks {
+        // Node A should build a block.
         node_a.harness.advance_chain_with_block();
+        // Node B should just increment it's slot without a block.
+        node_b.harness.increment_beacon_chain_slot();
     }
     node_a.harness.run_fork_choice();