diff --git a/internal/core/adt/composite.go b/internal/core/adt/composite.go
index b7db4fd1f..b41648ccb 100644
--- a/internal/core/adt/composite.go
+++ b/internal/core/adt/composite.go
@@ -851,6 +851,20 @@ func (v *Vertex) setValue(ctx *OpContext, state vertexStatus, value BaseValue) *
 	return nil
 }
 
+func (n *nodeContext) setBaseValue(value BaseValue) {
+	n.node.BaseValue = value
+}
+
+func (n *nodeContext) restoreBaseValue(value BaseValue) {
+	n.setBaseValue(value)
+}
+
+func (n *nodeContext) swapBaseValue(value BaseValue) (saved BaseValue) {
+	saved = n.node.BaseValue
+	n.setBaseValue(value)
+	return saved
+}
+
 // ToVertex wraps v in a new Vertex, if necessary.
 func ToVertex(v Value) *Vertex {
 	switch x := v.(type) {
diff --git a/internal/core/adt/context.go b/internal/core/adt/context.go
index 1e5b0b4f1..ceae3bab1 100644
--- a/internal/core/adt/context.go
+++ b/internal/core/adt/context.go
@@ -753,7 +753,7 @@ func (c *OpContext) evalState(v Expr, state combinedFlags) (result Value) {
 						}
 						err := c.Newf("cycle with field %v", x)
 						b := &Bottom{Code: CycleError, Err: err}
-						v.setValue(c, v.status, b)
+						s.setBaseValue(b)
 						return b
 						// TODO: use this instead, as is usual for incomplete errors,
 						// and also move this block one scope up to also apply to
diff --git a/internal/core/adt/cycle.go b/internal/core/adt/cycle.go
index c22c535e2..e6966b97b 100644
--- a/internal/core/adt/cycle.go
+++ b/internal/core/adt/cycle.go
@@ -611,14 +611,14 @@ func assertStructuralCycle(n *nodeContext) bool {
 }
 
 func (n *nodeContext) reportCycleError() {
-	n.node.BaseValue = CombineErrors(nil,
+	n.setBaseValue(CombineErrors(nil,
 		n.node.Value(),
 		&Bottom{
 			Code:  StructuralCycleError,
 			Err:   n.ctx.Newf("structural cycle"),
 			Value: n.node.Value(),
 			// TODO: probably, this should have the referenced arc.
-		})
+		}))
 	n.node.Arcs = nil
 }
 
diff --git a/internal/core/adt/disjunct.go b/internal/core/adt/disjunct.go
index ee9cc0e51..835f1d100 100644
--- a/internal/core/adt/disjunct.go
+++ b/internal/core/adt/disjunct.go
@@ -210,7 +210,7 @@ func (n *nodeContext) expandDisjuncts(
 			n.disjuncts = append(n.disjuncts, n)
 		}
 		if n.node.BaseValue == nil {
-			n.node.BaseValue = n.getValidators(state)
+			n.setBaseValue(n.getValidators(state))
 		}
 
 		n.usedDefault = append(n.usedDefault, defaultInfo{
diff --git a/internal/core/adt/disjunct2.go b/internal/core/adt/disjunct2.go
index b88625921..966a18894 100644
--- a/internal/core/adt/disjunct2.go
+++ b/internal/core/adt/disjunct2.go
@@ -317,7 +317,7 @@ func (n *nodeContext) processDisjunctions() *Bottom {
 
 	case 1:
 		d := cross[0].node
-		n.node.BaseValue = d
+		n.setBaseValue(d)
 		n.defaultMode = cross[0].defaultMode
 
 	default:
@@ -419,9 +419,7 @@ func (n *nodeContext) doDisjunct(c Conjunct, m defaultMode, mode runMode) (*node
 
 	v := d.node
 
-	saved := n.node.BaseValue
-	n.node.BaseValue = v
-	defer func() { n.node.BaseValue = saved }()
+	defer n.restoreBaseValue(n.swapBaseValue(v))
 
 	// Clear relevant scheduler states.
 	// TODO: do something more principled: just ensure that a node that has
@@ -487,7 +485,7 @@ func (n *nodeContext) finalizeDisjunctions() {
 	}
 
 	v := n.node
-	v.BaseValue = d
+	n.setBaseValue(d)
 
 	// The conjuncts will have too much information. Better have no
 	// information than incorrect information.
diff --git a/internal/core/adt/errors.go b/internal/core/adt/errors.go
index 44ef23804..8a77e9b48 100644
--- a/internal/core/adt/errors.go
+++ b/internal/core/adt/errors.go
@@ -131,7 +131,8 @@ func isIncomplete(v *Vertex) bool {
 //
 // If x is not already an error, the value is recorded in the error for
 // reference.
-func (v *Vertex) AddChildError(recursive *Bottom) {
+func (n *nodeContext) AddChildError(recursive *Bottom) {
+	v := n.node
 	v.ChildErrors = CombineErrors(nil, v.ChildErrors, recursive)
 	if recursive.IsIncomplete() {
 		return
@@ -139,13 +140,13 @@ func (v *Vertex) AddChildError(recursive *Bottom) {
 	x := v.BaseValue
 	err, _ := x.(*Bottom)
 	if err == nil {
-		v.BaseValue = &Bottom{
+		n.setBaseValue(&Bottom{
 			Code:         recursive.Code,
 			Value:        v,
 			HasRecursive: true,
 			ChildError:   true,
 			Err:          recursive.Err,
-		}
+		})
 		return
 	}
 
@@ -154,7 +155,7 @@ func (v *Vertex) AddChildError(recursive *Bottom) {
 		err.Code = recursive.Code
 	}
 
-	v.BaseValue = err
+	n.setBaseValue(err)
 }
 
 // CombineErrors combines two errors that originate at the same Vertex.
diff --git a/internal/core/adt/eval.go b/internal/core/adt/eval.go
index 9a50a09e1..67e379fd9 100644
--- a/internal/core/adt/eval.go
+++ b/internal/core/adt/eval.go
@@ -823,7 +823,7 @@ func (n *nodeContext) completeArcs(state vertexStatus) {
 				}
 
 				if err := a.Bottom(); err != nil {
-					n.node.AddChildError(err)
+					n.AddChildError(err)
 				}
 			}
 
diff --git a/internal/core/adt/tasks.go b/internal/core/adt/tasks.go
index 00412de8d..49c2bcd06 100644
--- a/internal/core/adt/tasks.go
+++ b/internal/core/adt/tasks.go
@@ -332,7 +332,7 @@ func (n *nodeContext) updateListType(list Expr, id CloseInfo, isClosed bool, ell
 		m = &ListMarker{
 			IsOpen: true,
 		}
-		n.node.setValue(n.ctx, conjuncts, m)
+		n.setBaseValue(m)
 	}
 	m.IsOpen = m.IsOpen && !isClosed
 
diff --git a/internal/core/adt/unify.go b/internal/core/adt/unify.go
index 65bdd2163..056bcf9a4 100644
--- a/internal/core/adt/unify.go
+++ b/internal/core/adt/unify.go
@@ -260,7 +260,7 @@ func (v *Vertex) unify(c *OpContext, needs condition, mode runMode) bool {
 		if b := n.node.Bottom(); b != nil {
 			err = CombineErrors(nil, b, err)
 		}
-		n.node.BaseValue = err
+		n.setBaseValue(err)
 	}
 
 	if mode == attemptOnly {
@@ -434,7 +434,7 @@ func (n *nodeContext) updateScalar() {
 	// Set BaseValue to scalar, but only if it was not set before. Most notably,
 	// errors should not be discarded.
 	if n.scalar != nil && (!n.node.IsErr() || isCyclePlaceholder(n.node.BaseValue)) {
-		n.node.BaseValue = n.scalar
+		n.setBaseValue(n.scalar)
 		n.signal(scalarKnown)
 	}
 }
@@ -521,7 +521,7 @@ func (n *nodeContext) completeAllArcs(needs condition, mode runMode) bool {
 		if !a.Label.IsLet() && a.ArcType <= ArcRequired {
 			a := a.DerefValue()
 			if err := a.Bottom(); err != nil {
-				n.node.AddChildError(err)
+				n.AddChildError(err)
 			}
 			success = true // other arcs are irrelevant
 		}