diff --git a/autopilot/combinedattach.go b/autopilot/combinedattach.go
index f61ba33e..6f982b79 100644
--- a/autopilot/combinedattach.go
+++ b/autopilot/combinedattach.go
@@ -25,7 +25,7 @@ type WeightedCombAttachment struct {
 
 // NewWeightedCombAttachment creates a new instance of a WeightedCombAttachment.
 func NewWeightedCombAttachment(h ...*WeightedHeuristic) (
-	AttachmentHeuristic, error) {
+	*WeightedCombAttachment, error) {
 
 	// The sum of weights given to the sub-heuristics must sum to exactly
 	// 1.0.
@@ -44,8 +44,9 @@ func NewWeightedCombAttachment(h ...*WeightedHeuristic) (
 }
 
 // A compile time assertion to ensure WeightedCombAttachment meets the
-// AttachmentHeuristic interface.
+// AttachmentHeuristic and ScoreSettable interfaces.
 var _ AttachmentHeuristic = (*WeightedCombAttachment)(nil)
+var _ ScoreSettable = (*WeightedCombAttachment)(nil)
 
 // Name returns the name of this heuristic.
 //
@@ -135,6 +136,8 @@ func (c *WeightedCombAttachment) NodeScores(g ChannelGraph, chans []Channel,
 //
 // Since this heuristic doesn't keep any internal scores, it will recursively
 // apply the scores to its sub-heuristics.
+//
+// NOTE: This is a part of the ScoreSettable interface.
 func (c *WeightedCombAttachment) SetNodeScores(targetHeuristic string,
 	newScores map[NodeID]float64) (bool, error) {
 
diff --git a/autopilot/externalscoreattach.go b/autopilot/externalscoreattach.go
index 817ca769..68fae308 100644
--- a/autopilot/externalscoreattach.go
+++ b/autopilot/externalscoreattach.go
@@ -23,8 +23,9 @@ func NewExternalScoreAttachment() *ExternalScoreAttachment {
 }
 
 // A compile time assertion to ensure ExternalScoreAttachment meets the
-// AttachmentHeuristic interface.
+// AttachmentHeuristic and ScoreSettable interfaces.
 var _ AttachmentHeuristic = (*ExternalScoreAttachment)(nil)
+var _ ScoreSettable = (*ExternalScoreAttachment)(nil)
 
 // Name returns the name of this heuristic.
 //
@@ -38,6 +39,8 @@ func (s *ExternalScoreAttachment) Name() string {
 // of the targeted heuristic, to allow recursively target specific
 // sub-heuristics. The returned boolean indicates whether the targeted
 // heuristic was found.
+//
+// NOTE: This is a part of the ScoreSettable interface.
 func (s *ExternalScoreAttachment) SetNodeScores(targetHeuristic string,
 	newScores map[NodeID]float64) (bool, error) {
 
diff --git a/autopilot/interface.go b/autopilot/interface.go
index 04a2ecdc..1886929a 100644
--- a/autopilot/interface.go
+++ b/autopilot/interface.go
@@ -142,6 +142,21 @@ type AttachmentHeuristic interface {
 		map[NodeID]*NodeScore, error)
 }
 
+// ScoreSettable is an interface that indicates that the scores returned by the
+// heuristic can be mutated by an external caller. The ExternalScoreAttachment
+// currently implements this interface, and so should any heuristic that is
+// using the ExternalScoreAttachment as a sub-heuristic, or keeps their own
+// internal list of mutable scores, to allow access to setting the internal
+// scores.
+type ScoreSettable interface {
+	// SetNodeScores is used to set the internal map from NodeIDs to
+	// scores. The passed scores must be in the range [0, 1.0]. The fist
+	// parameter is the name of the targeted heuristic, to allow
+	// recursively target specific sub-heuristics. The returned boolean
+	// indicates whether the targeted heuristic was found.
+	SetNodeScores(string, map[NodeID]float64) (bool, error)
+}
+
 var (
 	// availableHeuristics holds all heuristics possible to combine for use
 	// with the autopilot agent.