diff --git a/internal/netsync/manager.go b/internal/netsync/manager.go
index 3f0911668..2b3504101 100644
--- a/internal/netsync/manager.go
+++ b/internal/netsync/manager.go
@@ -338,7 +338,7 @@ type SyncManager struct {
 	rejectedTxns     *apbf.Filter
 	rejectedMixMsgs  *apbf.Filter
 	requestedTxns    map[chainhash.Hash]struct{}
-	requestedBlocks  map[chainhash.Hash]struct{}
+	requestedBlocks  map[chainhash.Hash]*Peer
 	requestedMixMsgs map[chainhash.Hash]struct{}
 	progressLogger   *progresslog.Logger
 	syncPeer         *Peer
@@ -424,6 +424,16 @@ func (m *SyncManager) maybeUpdateNextNeededBlocks() {
 	}
 }
 
+// isRequestedBlock returns whether or not the given block hash has already been
+// requested from any remote peer.
+//
+// This function is NOT safe for concurrent access.  It must be called from the
+// event handler goroutine.
+func (m *SyncManager) isRequestedBlock(hash *chainhash.Hash) bool {
+	_, ok := m.requestedBlocks[*hash]
+	return ok
+}
+
 // fetchNextBlocks creates and sends a request to the provided peer for the next
 // blocks to be downloaded based on the current headers.
 func (m *SyncManager) fetchNextBlocks(peer *Peer) {
@@ -458,12 +468,12 @@ func (m *SyncManager) fetchNextBlocks(peer *Peer) {
 		// Skip blocks that have already been requested.  The needed blocks
 		// might have been updated above thereby potentially repopulating some
 		// blocks that are still in flight.
-		if _, ok := m.requestedBlocks[*hash]; ok {
+		if m.isRequestedBlock(hash) {
 			continue
 		}
 
 		iv := wire.NewInvVect(wire.InvTypeBlock, hash)
-		m.requestedBlocks[*hash] = struct{}{}
+		m.requestedBlocks[*hash] = peer
 		peer.requestedBlocks[*hash] = struct{}{}
 		gdmsg.AddInvVect(iv)
 	}
@@ -1454,14 +1464,19 @@ func (m *SyncManager) handleHeadersMsg(hmsg *headersMsg) {
 			// Skip the block when it has already been requested or is otherwise
 			// already known.
 			hash := &headerHashes[i]
-			_, isRequestedBlock := m.requestedBlocks[*hash]
-			if isRequestedBlock || chain.HaveBlock(hash) {
+			if m.isRequestedBlock(hash) || chain.HaveBlock(hash) {
 				continue
 			}
 
+			// Stop requesting when the request would exceed the max size of the
+			// map used to track requests.
+			if len(m.requestedBlocks)+1 > maxRequestedBlocks {
+				break
+			}
+
+			m.requestedBlocks[*hash] = peer
+			peer.requestedBlocks[*hash] = struct{}{}
 			iv := wire.NewInvVect(wire.InvTypeBlock, hash)
-			limitAdd(m.requestedBlocks, *hash, maxRequestedBlocks)
-			limitAdd(peer.requestedBlocks, *hash, maxRequestedBlocks)
 			gdmsg.AddInvVect(iv)
 		}
 		if len(gdmsg.InvList) > 0 {
@@ -1920,12 +1935,9 @@ func (m *SyncManager) requestFromPeer(peer *Peer, blocks, voteHashes,
 	// Add the blocks to the request.
 	msgResp := wire.NewMsgGetData()
 	for i := range blocks {
-		// If we've already requested this block, skip it.
+		// Skip the block when it has already been requested.
 		bh := &blocks[i]
-		_, alreadyReqP := peer.requestedBlocks[*bh]
-		_, alreadyReqB := m.requestedBlocks[*bh]
-
-		if alreadyReqP || alreadyReqB {
+		if m.isRequestedBlock(bh) {
 			continue
 		}
 
@@ -1942,7 +1954,7 @@ func (m *SyncManager) requestFromPeer(peer *Peer, blocks, voteHashes,
 		}
 
 		peer.requestedBlocks[*bh] = struct{}{}
-		m.requestedBlocks[*bh] = struct{}{}
+		m.requestedBlocks[*bh] = peer
 	}
 
 	addTxsToRequest := func(txs []chainhash.Hash, txType stake.TxType) error {
@@ -2169,7 +2181,7 @@ func New(config *Config) *SyncManager {
 		rejectedTxns:     apbf.NewFilter(maxRejectedTxns, rejectedTxnsFPRate),
 		rejectedMixMsgs:  apbf.NewFilter(maxRejectedMixMsgs, rejectedMixMsgsFPRate),
 		requestedTxns:    make(map[chainhash.Hash]struct{}),
-		requestedBlocks:  make(map[chainhash.Hash]struct{}),
+		requestedBlocks:  make(map[chainhash.Hash]*Peer),
 		requestedMixMsgs: make(map[chainhash.Hash]struct{}),
 		peers:            make(map[*Peer]struct{}),
 		minKnownWork:     minKnownWork,