diff --git a/runtime/src/accounts_db.rs b/runtime/src/accounts_db.rs
index 4b8ab84bf169ab..7d46cddecb56cb 100644
--- a/runtime/src/accounts_db.rs
+++ b/runtime/src/accounts_db.rs
@@ -9115,7 +9115,7 @@ impl AccountsDb {
                     // get duplicate keys from acct idx. We have to wait until we've finished flushing.
                     for (slot, key) in self
                         .accounts_index
-                        .retrieve_duplicate_keys_from_startup()
+                        .populate_and_retrieve_duplicate_keys_from_startup()
                         .into_iter()
                         .flatten()
                     {
diff --git a/runtime/src/accounts_index.rs b/runtime/src/accounts_index.rs
index a29d91ef2f632a..44afd7535d638b 100644
--- a/runtime/src/accounts_index.rs
+++ b/runtime/src/accounts_index.rs
@@ -1685,11 +1685,14 @@ impl<T: IndexValue, U: DiskIndexValue + From<T> + Into<T>> AccountsIndex<T, U> {
     }
 
     /// return Vec<Vec<>> because the internal vecs are already allocated per bin
-    pub fn retrieve_duplicate_keys_from_startup(&self) -> Vec<Vec<(Slot, Pubkey)>> {
+    pub(crate) fn populate_and_retrieve_duplicate_keys_from_startup(
+        &self,
+    ) -> Vec<Vec<(Slot, Pubkey)>> {
         (0..self.bins())
+            .into_par_iter()
             .map(|pubkey_bin| {
                 let r_account_maps = &self.account_maps[pubkey_bin];
-                r_account_maps.retrieve_duplicate_keys_from_startup()
+                r_account_maps.populate_and_retrieve_duplicate_keys_from_startup()
             })
             .collect()
     }
@@ -2699,6 +2702,7 @@ pub mod tests {
             index.set_startup(Startup::Normal);
         }
         assert!(gc.is_empty());
+        index.populate_and_retrieve_duplicate_keys_from_startup();
 
         for lock in &[false, true] {
             let read_lock = if *lock {
diff --git a/runtime/src/in_mem_accounts_index.rs b/runtime/src/in_mem_accounts_index.rs
index 1641d278f20168..7ab9847856c381 100644
--- a/runtime/src/in_mem_accounts_index.rs
+++ b/runtime/src/in_mem_accounts_index.rs
@@ -13,7 +13,7 @@ use {
     solana_measure::measure::Measure,
     solana_sdk::{clock::Slot, pubkey::Pubkey},
     std::{
-        collections::{hash_map::Entry, HashMap},
+        collections::{hash_map::Entry, HashMap, HashSet},
         fmt::Debug,
         ops::{Bound, RangeBounds, RangeInclusive},
         sync::{
@@ -128,8 +128,11 @@ pub enum InsertNewEntryResults {
 struct StartupInfo<T: IndexValue> {
     /// entries to add next time we are flushing to disk
     insert: Vec<(Slot, Pubkey, T)>,
-    /// pubkeys that were found to have duplicate index entries
-    duplicates: Vec<(Slot, Pubkey)>,
+    /// entries that were found to have duplicate index entries.
+    /// When all entries have been inserted, these can be resolved and held in memory.
+    duplicates: Vec<(Slot, Pubkey, T)>,
+    /// pubkeys that were already added to disk and later found to be duplicates,
+    duplicates_put_on_disk: HashSet<(Slot, Pubkey)>,
 }
 
 #[derive(Default, Debug)]
@@ -1040,7 +1043,8 @@ impl<T: IndexValue, U: DiskIndexValue + From<T> + Into<T>> InMemAccountsIndex<T,
         );
         drop(map_internal);
 
-        let mut duplicates = vec![];
+        // this fn should only be called from a single thread, so holding the lock is fine
+        let mut startup_info = self.startup_info.lock().unwrap();
 
         // merge all items into the disk index now
         let disk = self.bucket.as_ref().unwrap();
@@ -1050,21 +1054,16 @@ impl<T: IndexValue, U: DiskIndexValue + From<T> + Into<T>> InMemAccountsIndex<T,
             let new_ref_count = u64::from(!v.is_cached());
             disk.update(&k, |current| {
                 match current {
-                    Some((current_slot_list, mut ref_count)) => {
-                        // merge this in, mark as duplicate
-                        duplicates.push((slot, k));
-                        if current_slot_list.len() == 1 {
+                    Some((current_slot_list, ref_count)) => {
+                        // already on disk, so remember the new (slot, info) for later
+                        startup_info.duplicates.push((slot, k, entry.1));
+                        if let Some((slot, _)) = current_slot_list.first() {
                             // accurately account for there being a duplicate for the first entry that was previously added to the disk index.
                             // That entry could not have known yet that it was a duplicate.
                             // It is important to capture each slot with a duplicate because of slot limits applied to clean.
-                            let first_entry_slot = current_slot_list[0].0;
-                            duplicates.push((first_entry_slot, k));
+                            startup_info.duplicates_put_on_disk.insert((*slot, k));
                         }
-                        let mut slot_list = Vec::with_capacity(current_slot_list.len() + 1);
-                        slot_list.extend_from_slice(current_slot_list);
-                        slot_list.push((entry.0, entry.1.into())); // will never be from the same slot that already exists in the list
-                        ref_count += new_ref_count;
-                        Some((slot_list, ref_count))
+                        Some((current_slot_list.to_vec(), ref_count))
                     }
                     None => {
                         count += 1;
@@ -1075,22 +1074,28 @@ impl<T: IndexValue, U: DiskIndexValue + From<T> + Into<T>> InMemAccountsIndex<T,
             });
         });
         self.stats().inc_insert_count(count);
-        self.startup_info
-            .lock()
-            .unwrap()
-            .duplicates
-            .append(&mut duplicates);
     }
 
     /// pull out all duplicate pubkeys from 'startup_info'
     /// duplicate pubkeys have a slot list with len > 1
     /// These were collected for this bin when we did batch inserts in the bg flush threads.
-    pub fn retrieve_duplicate_keys_from_startup(&self) -> Vec<(Slot, Pubkey)> {
+    /// Insert these into the in-mem index, then return the duplicate (Slot, Pubkey)
+    pub(crate) fn populate_and_retrieve_duplicate_keys_from_startup(&self) -> Vec<(Slot, Pubkey)> {
         let mut write = self.startup_info.lock().unwrap();
         // in order to return accurate and complete duplicates, we must have nothing left remaining to insert
         assert!(write.insert.is_empty());
 
-        std::mem::take(&mut write.duplicates)
+        let duplicates = std::mem::take(&mut write.duplicates);
+        let duplicates_put_on_disk = std::mem::take(&mut write.duplicates_put_on_disk);
+        drop(write);
+        duplicates_put_on_disk
+            .into_iter()
+            .chain(duplicates.into_iter().map(|(slot, key, info)| {
+                let entry = PreAllocatedAccountMapEntry::new(slot, info, &self.storage, true);
+                self.insert_new_entry_if_missing_with_lock(key, entry);
+                (slot, key)
+            }))
+            .collect()
     }
 
     /// synchronize the in-mem index with the disk index