diff --git a/src/Chainweb/Mempool/InMem.hs b/src/Chainweb/Mempool/InMem.hs
index 2c86640c5b..84c2a527be 100644
--- a/src/Chainweb/Mempool/InMem.hs
+++ b/src/Chainweb/Mempool/InMem.hs
@@ -34,7 +34,7 @@ import Control.Concurrent.Async
 import Control.Concurrent.MVar
 import Control.DeepSeq
 import Control.Error.Util (hush)
-import Control.Exception (evaluate, mask_, throw)
+import Control.Exception (evaluate, mask_, throw, bracket_)
 import Control.Monad
 
 import qualified Data.ByteString.Short as SB
@@ -47,7 +47,7 @@ import Data.Foldable (foldl', foldlM)
 import Data.Function (on)
 import Data.HashMap.Strict (HashMap)
 import qualified Data.HashMap.Strict as HashMap
-import Data.IORef (modifyIORef', newIORef, readIORef, writeIORef)
+import Data.IORef
 import Data.Maybe
 import Data.Ord
 import qualified Data.Set as S
@@ -84,6 +84,8 @@ import Numeric.AffineSpace
 import Data.ByteString (ByteString)
 import Data.Either (partitionEithers)
 import Control.Lens
+import Data.HashSet (HashSet)
+import qualified Data.HashSet as HashSet
 
 ------------------------------------------------------------------------------
 compareOnGasPrice :: TransactionConfig t -> t -> t -> Ordering
@@ -100,7 +102,8 @@ makeInMemPool :: InMemConfig t
 makeInMemPool cfg = mask_ $ do
     nonce <- randomIO
     dataLock <- newInMemMempoolData >>= newMVar
-    return $! InMemoryMempool cfg dataLock nonce
+    pendingInsertionRef <- newIORef mempty
+    return $! InMemoryMempool cfg dataLock pendingInsertionRef nonce
 
 
 ------------------------------------------------------------------------------
@@ -126,7 +129,7 @@ toMempoolBackend logger mempool = do
       , mempoolMember = memberInMem lockMVar
       , mempoolLookup = lookupInMem tcfg lockMVar
       , mempoolLookupEncoded = lookupEncodedInMem lockMVar
-      , mempoolInsert = insertInMem logger cfg lockMVar
+      , mempoolInsert = insertInMem logger cfg (_inmemInsertionPending mempool) lockMVar
       , mempoolInsertCheck = insertCheckInMem cfg lockMVar
       , mempoolInsertCheckVerbose = insertCheckVerboseInMem cfg lockMVar
       , mempoolMarkValidated = markValidatedInMem logger tcfg lockMVar
@@ -500,7 +503,7 @@ insertCheckInMem'
     .  NFData t
     => InMemConfig t    -- ^ in-memory config
     -> MVar (InMemoryMempoolData t)  -- ^ in-memory state
-    -> Vector t  -- ^ new transactions
+    -> Vector (T2 TransactionHash t)  -- ^ new transactions
     -> IO (Vector (T2 TransactionHash t))
 insertCheckInMem' cfg lock txs
   | V.null txs = pure V.empty
@@ -510,42 +513,54 @@ insertCheckInMem' cfg lock txs
     curTxIdx <- withMVarMasked lock $ readIORef . _inmemCurrentTxs
 
     let withHashes :: Vector (T2 TransactionHash t)
-        withHashes = flip V.mapMaybe txs $ \tx ->
-          let !h = hasher tx
-          in (T2 h) <$> hush (validateOne cfg badmap curTxIdx now tx h)
+        withHashes = flip V.mapMaybe txs $ \(T2 h tx) ->
+          T2 h <$> hush (validateOne cfg badmap curTxIdx now tx h)
 
     V.mapMaybe hush <$!> _inmemPreInsertBatchChecks cfg withHashes
-  where
-    txcfg = _inmemTxCfg cfg
-    hasher = txHasher txcfg
 
 insertInMem
     :: forall t logger. (NFData t, Logger logger)
     => logger
     -> InMemConfig t    -- ^ in-memory config
+    -> IORef (HashSet TransactionHash)
     -> MVar (InMemoryMempoolData t)  -- ^ in-memory state
     -> InsertType
     -> Vector t  -- ^ new transactions
     -> IO ()
-insertInMem logger cfg lock runCheck txs0 = do
-    logFunctionText logger Debug $ "insertInMem: " <> sshow (runCheck, V.length txs0)
-    txhashes <- insertCheck
-    withMVarMasked lock $ \mdata -> do
-        pending <- readIORef (_inmemPending mdata)
-        logFunctionText logger Debug $ "insertInMem: pending txs: " <> sshow (HashMap.keys pending)
-        let cnt = HashMap.size pending
-        let txs = V.take (max 0 (maxNumPending - cnt)) txhashes
-        let T2 !pending' !newHashesDL = V.foldl' insOne (T2 pending id) txs
-        logFunctionText logger Debug $ "insertInMem: updated pending txs: " <> sshow (HashMap.keys pending')
-        let !newHashes = V.fromList $ newHashesDL []
-        writeIORef (_inmemPending mdata) $! force pending'
-        modifyIORef' (_inmemRecentLog mdata) $
-            recordRecentTransactions maxRecent newHashes
+insertInMem logger cfg pendingInsertionRef lock runCheck txs0 = do
+    pendingInsertionsDirty <- readIORef pendingInsertionRef
+    let
+      txs' = flip V.mapMaybe txs0 $ \tx ->
+        let hash = hasher tx
+        in if not (HashSet.member hash pendingInsertionsDirty)
+        then Just (T2 hash tx)
+        else Nothing
+    bracket_
+      (atomicModifyIORef' pendingInsertionRef $ \pendingInsertions ->
+        (foldl' (flip HashSet.insert) pendingInsertions (sfst <$> txs'), ()))
+      (do
+        logFunctionText logger Debug $ "insertInMem: " <> sshow (runCheck, V.length txs')
+        txhashes <- insertCheck txs'
+        withMVarMasked lock $ \mdata -> do
+            pending <- readIORef (_inmemPending mdata)
+            logFunctionText logger Debug $ "insertInMem: pending txs: " <> sshow (HashMap.keys pending)
+            let cnt = HashMap.size pending
+            let txs = V.take (max 0 (maxNumPending - cnt)) txhashes
+            let T2 !pending' !newHashesDL = V.foldl' insOne (T2 pending id) txs
+            logFunctionText logger Debug $ "insertInMem: updated pending txs: " <> sshow (HashMap.keys pending')
+            let !newHashes = V.fromList $ newHashesDL []
+            writeIORef (_inmemPending mdata) $! force pending'
+            modifyIORef' (_inmemRecentLog mdata) $
+                recordRecentTransactions maxRecent newHashes
+      )
+      (atomicModifyIORef' pendingInsertionRef $ \pendingInsertions ->
+        (foldl' (flip HashSet.delete) pendingInsertions (sfst <$> txs'), ()))
+
   where
-    insertCheck :: IO (Vector (T2 TransactionHash t))
-    insertCheck = case runCheck of
-      CheckedInsert -> insertCheckInMem' cfg lock txs0
-      UncheckedInsert -> return $! V.map (\tx -> T2 (hasher tx) tx) txs0
+    insertCheck :: Vector (T2 TransactionHash t) -> IO (Vector (T2 TransactionHash t))
+    insertCheck txs' = case runCheck of
+      CheckedInsert -> insertCheckInMem' cfg lock txs'
+      UncheckedInsert -> return txs'
 
     txcfg = _inmemTxCfg cfg
     encodeTx = codecEncode (txCodec txcfg)
diff --git a/src/Chainweb/Mempool/InMemTypes.hs b/src/Chainweb/Mempool/InMemTypes.hs
index e95fb936e8..8130124e20 100644
--- a/src/Chainweb/Mempool/InMemTypes.hs
+++ b/src/Chainweb/Mempool/InMemTypes.hs
@@ -43,6 +43,7 @@ import Chainweb.Mempool.CurrentTxs
 import Chainweb.Mempool.Mempool
 import Chainweb.Time (Micros(..), Time(..))
 import Chainweb.Utils (T2)
+import Data.HashSet (HashSet)
 
 ------------------------------------------------------------------------------
 data PendingEntry = PendingEntry
@@ -80,6 +81,7 @@ data InMemConfig t = InMemConfig {
 data InMemoryMempool t = InMemoryMempool {
     _inmemCfg :: !(InMemConfig t)
   , _inmemDataLock :: !(MVar (InMemoryMempoolData t))
+  , _inmemInsertionPending :: !(IORef (HashSet TransactionHash))
   , _inmemNonce :: !ServerNonce
 }