diff --git a/CHANGELOG.md b/CHANGELOG.md
index 972ecefed..2a48f917c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -22,8 +22,8 @@ The following emojis are used to highlight certain changes:
 
 ### Fixed
 
-`bitswap/client`: Fix runaway goroutine creation under high load. Under high load conditions, goroutines are created faster than they can complete and the more goroutines creates the slower them complete. This creates a positive feedback cycle that ends in OOM. The fix dynamically adjusts message send scheduling to avoid the runaway condition. [#817](https://github.com/ipfs/boxo/pull/817)
-
+- `bitswap/client`: Fix runaway goroutine creation under high load. Under high load conditions, goroutines are created faster than they can complete and the more goroutines creates the slower them complete. This creates a positive feedback cycle that ends in OOM. The fix dynamically adjusts message send scheduling to avoid the runaway condition. [#817](https://github.com/ipfs/boxo/pull/817)
+- `bitswap/cllient`: Fix resource leak caused by recording the presence of blocks that no session cares about. [#822](https://github.com/ipfs/boxo/pull/822)
 
 ### Security
 
diff --git a/bitswap/client/internal/sessioninterestmanager/sessioninterestmanager.go b/bitswap/client/internal/sessioninterestmanager/sessioninterestmanager.go
index 6d63300e8..94ec20923 100644
--- a/bitswap/client/internal/sessioninterestmanager/sessioninterestmanager.go
+++ b/bitswap/client/internal/sessioninterestmanager/sessioninterestmanager.go
@@ -120,10 +120,11 @@ func (sim *SessionInterestManager) FilterSessionInterested(ses uint64, ksets ...
 // When bitswap receives blocks it calls SplitWantedUnwanted() to discard
 // unwanted blocks
 func (sim *SessionInterestManager) SplitWantedUnwanted(blks []blocks.Block) ([]blocks.Block, []blocks.Block) {
-	sim.lk.RLock()
-
 	// Get the wanted block keys as a set
 	wantedKs := cid.NewSet()
+
+	sim.lk.RLock()
+
 	for _, b := range blks {
 		c := b.Cid()
 		// For each session that wants the key.
@@ -139,7 +140,7 @@ func (sim *SessionInterestManager) SplitWantedUnwanted(blks []blocks.Block) ([]b
 
 	// Separate the blocks into wanted and unwanted
 	wantedBlks := make([]blocks.Block, 0, len(blks))
-	notWantedBlks := make([]blocks.Block, 0)
+	var notWantedBlks []blocks.Block
 	for _, b := range blks {
 		if wantedKs.Has(b.Cid()) {
 			wantedBlks = append(wantedBlks, b)
@@ -176,12 +177,17 @@ func (sim *SessionInterestManager) InterestedSessions(keySets ...[]cid.Cid) []ui
 	return ses
 }
 
-// Filters only the keys that are wanted by at least one session
+// Filters only the keys that are wanted by at least one session.
+//
+// IMPORTANT: FilterInterests filters the given Cid slices in place, modifying
+// their contents. If the caller needs to preserve a copy of the lists it
+// should make a copy before calling FilterInterests.
 func (sim *SessionInterestManager) FilterInterests(keySets ...[]cid.Cid) [][]cid.Cid {
+	result := keySets[:0]
+
 	sim.lk.RLock()
 	defer sim.lk.RUnlock()
 
-	result := keySets[:0]
 	// For each set of keys
 	for _, ks := range keySets {
 		// The set of keys wanted by at least one session
diff --git a/bitswap/client/internal/sessionmanager/sessionmanager.go b/bitswap/client/internal/sessionmanager/sessionmanager.go
index 88942c14e..112a2764d 100644
--- a/bitswap/client/internal/sessionmanager/sessionmanager.go
+++ b/bitswap/client/internal/sessionmanager/sessionmanager.go
@@ -151,7 +151,11 @@ func (sm *SessionManager) GetNextSessionID() uint64 {
 	return sm.sessID
 }
 
-// ReceiveFrom is called when a new message is received
+// ReceiveFrom is called when a new message is received.
+//
+// IMPORTANT: ReceiveFrom filters the given Cid slices in place, modifying
+// their contents. If the caller needs to preserve a copy of the lists it
+// should make a copy before calling ReceiveFrom.
 func (sm *SessionManager) ReceiveFrom(ctx context.Context, p peer.ID, blks []cid.Cid, haves []cid.Cid, dontHaves []cid.Cid) {
 	// Keep only the keys that at least one session wants
 	keys := sm.sessionInterestManager.FilterInterests(blks, haves, dontHaves)