diff --git a/traversal/operation.go b/traversal/operation.go
index 9839fbc53..90abd8807 100644
--- a/traversal/operation.go
+++ b/traversal/operation.go
@@ -2,6 +2,7 @@ package traversal
 
 import (
 	"context"
+	"errors"
 	"sync/atomic"
 
 	"github.com/anacrolix/chansync"
@@ -121,20 +122,35 @@ func (op *Operation) Stalled() events.Active {
 	return op.stalled.Active()
 }
 
+func (op *Operation) addNodeLocked(n types.AddrMaybeId) (err error) {
+	if _, ok := op.queried[addrString(n.Addr.String())]; ok {
+		err = errors.New("already queried")
+		return
+	}
+	if !op.input.NodeFilter(n) {
+		err = errors.New("failed filter")
+		return
+	}
+	op.unqueried = op.unqueried.Add(n)
+	op.cond.Broadcast()
+	return nil
+}
+
+// Add an unqueried node returning an error with a reason why the node wasn't added.
+func (op *Operation) AddNode(n types.AddrMaybeId) (err error) {
+	op.mu.Lock()
+	defer op.mu.Unlock()
+	return op.addNodeLocked(n)
+}
+
+// Add a bunch of unqueried nodes at once, returning how many were successfully added.
 func (op *Operation) AddNodes(nodes []types.AddrMaybeId) (added int) {
 	op.mu.Lock()
 	defer op.mu.Unlock()
 	before := op.unqueried.Len()
 	for _, n := range nodes {
-		if _, ok := op.queried[addrString(n.Addr.String())]; ok {
-			continue
-		}
-		if !op.input.NodeFilter(n) {
-			continue
-		}
-		op.unqueried = op.unqueried.Add(n)
+		_ = op.addNodeLocked(n)
 	}
-	op.cond.Broadcast()
 	return op.unqueried.Len() - before
 }