diff --git a/codex/blockexchange/engine/engine.nim b/codex/blockexchange/engine/engine.nim
index 73b5442c..80986e70 100644
--- a/codex/blockexchange/engine/engine.nim
+++ b/codex/blockexchange/engine/engine.nim
@@ -18,6 +18,7 @@ import pkg/libp2p/[cid, switch, multihash, multicodec]
 import pkg/metrics
 import pkg/stint
 import pkg/questionable
+import pkg/stew/shims/sets
 
 import ../../rng
 import ../../stores/blockstore
@@ -297,47 +298,31 @@ proc blockPresenceHandler*(
   trace "Received block presence from peer", peer, len = blocks.len
   let
     peerCtx = self.peers.get(peer)
-    ourWantList = toSeq(self.pendingBlocks.wantList)
+    ourWantList = toHashSet(self.pendingBlocks.wantList.toSeq)
 
   if peerCtx.isNil:
     return
 
-  trace "Build presence list"
-
   for blk in blocks:
     if presence =? Presence.init(blk):
       peerCtx.setPresence(presence)
 
-  trace "Built presence list"
-
-  trace "Remove dont want cids"
-
   let
-    peerHave = peerCtx.peerHave
-    dontWantCids = peerHave.filterIt(it notin ourWantList)
-
-  trace "Removed dont want cids"
+    peerHave = peerCtx.peerHave.toHashSet
+    dontWantCids = peerHave - ourWantList
 
   if dontWantCids.len > 0:
-    peerCtx.cleanPresence(dontWantCids)
-
-  trace "Remove want cids"
+    peerCtx.cleanPresence(dontWantCids.toSeq)
 
   let ourWantCids = ourWantList.filterIt(
     it in peerHave and not self.pendingBlocks.retriesExhausted(it) and
       not self.pendingBlocks.isInFlight(it)
-  )
-
-  trace "Removed want cids"
-
-  trace "Update pending blocks"
+  ).toSeq
 
   for address in ourWantCids:
     self.pendingBlocks.setInFlight(address, true)
     self.pendingBlocks.decRetries(address)
 
-  trace "Updated pending blocks"
-
   if ourWantCids.len > 0:
     trace "Peer has blocks in our wantList", peer, wants = ourWantCids
     # FIXME: this will result in duplicate requests for blocks
diff --git a/codex/blockexchange/peers/peercontext.nim b/codex/blockexchange/peers/peercontext.nim
index a4b0329a..efac8b43 100644
--- a/codex/blockexchange/peers/peercontext.nim
+++ b/codex/blockexchange/peers/peercontext.nim
@@ -34,7 +34,7 @@ type BlockExcPeerCtx* = ref object of RootObj
   lastRefresh*: Moment # last time we refreshed our knowledge of the blocks this peer has
   account*: ?Account # ethereum account of this peer
   paymentChannel*: ?ChannelId # payment channel id
-  blocksInFlight*: seq[BlockAddress] # blocks in flight towards peer
+  blocksInFlight*: HashSet[BlockAddress] # blocks in flight towards peer
 
 proc isKnowledgeStale*(self: BlockExcPeerCtx): bool =
   self.lastRefresh + 15.seconds < Moment.now()
@@ -43,13 +43,10 @@ proc isInFlight*(self: BlockExcPeerCtx, address: BlockAddress): bool =
   address in self.blocksInFlight
 
 proc addInFlight*(self: BlockExcPeerCtx, address: BlockAddress) =
-  if not self.isInFlight(address):
-    self.blocksInFlight.add(address)
+  self.blocksInFlight.incl(address)
 
 proc removeInFlight*(self: BlockExcPeerCtx, address: BlockAddress) =
-  let index = self.blocksInFlight.find(address)
-  if index != -1:
-    self.blocksInFlight.delete(index)
+  self.blocksInFlight.excl(address)
 
 proc refreshed*(self: BlockExcPeerCtx) =
   self.lastRefresh = Moment.now()