diff --git a/internal/ast/ast.go b/internal/ast/ast.go
index 0cd9f93..a8727e3 100644
--- a/internal/ast/ast.go
+++ b/internal/ast/ast.go
@@ -76,47 +76,90 @@ type Root []Node
 // Dot returns a dot representation of the AST for debugging.
 func (r Root) Sdot() string {
 	type edge struct {
-		from int
-		to   int
+		from     int
+		childIdx int
+		to       int
 	}
 
-	var nodes []string
+	var nodes []Node
 	var edges []edge // indexes into nodes
 
-	nodes = append(nodes, "root")
+	nodes = append(nodes, Node{
+		Kind:     Invalid,
+		Data:     []byte(`ROOT`),
+		Children: r,
+	})
 
-	labelForNode := func(node *Node) string {
-		return fmt.Sprintf("{%s}", node.Kind)
-	}
-
-	var processNode func(int, *Node)
-	processNode = func(parentIdx int, node *Node) {
+	var processNode func(int, int, *Node)
+	processNode = func(parentIdx int, childIdx int, node *Node) {
 		idx := len(nodes)
-		label := labelForNode(node)
-		nodes = append(nodes, label)
-		edges = append(edges, edge{from: parentIdx, to: idx})
+		nodes = append(nodes, *node)
+		edges = append(edges, edge{
+			from:     parentIdx,
+			childIdx: childIdx,
+			to:       idx,
+		})
 
-		for _, c := range node.Children {
-			processNode(idx, &c)
+		for i, c := range node.Children {
+			processNode(idx, i, &c)
 		}
 	}
 
-	for _, n := range r {
-		processNode(0, &n)
+	for i, n := range r {
+		processNode(0, i, &n)
 	}
 
 	var b strings.Builder
 
 	b.WriteString("digraph tree {\n")
+	b.WriteString("\tnode [shape=record];\n")
 
-	for i, label := range nodes {
-		_, _ = fmt.Fprintf(&b, "\tnode%d [label=\"%s\"];\n", i, label)
+	for i, node := range nodes {
+		label := ""
+		attrs := map[string]string{}
+
+		if i == 0 {
+			var ports []string
+			for i := 0; i < len(node.Children); i++ {
+				ports = append(ports, fmt.Sprintf("<f%d> %d", i, i))
+			}
+			joinedPorts := strings.Join(ports, "|")
+			label = fmt.Sprintf("{ROOT|{%s}}", joinedPorts)
+		} else {
+			fields := []string{node.Kind.String()}
+			if len(node.Data) > 0 {
+				fields = append(fields, string(node.Data))
+			}
+
+			var ports []string
+			for i := 0; i < len(node.Children); i++ {
+				ports = append(ports, fmt.Sprintf("<f%d> %d", i, i))
+			}
+			joinedPorts := strings.Join(ports, "|")
+
+			joinedFields := strings.Join(fields, "|")
+			label = fmt.Sprintf("{{%s}", joinedFields)
+			if len(ports) > 0 {
+				label += fmt.Sprintf("|{%s}", joinedPorts)
+			}
+			label += "}"
+			if node.Kind == Invalid {
+				attrs["style"] = "filled"
+				attrs["fillcolor"] = "red"
+			}
+		}
+
+		_, _ = fmt.Fprintf(&b, "\tnode%d [label=\"%s\"", i, label)
+		for k, v := range attrs {
+			_, _ = fmt.Fprintf(&b, ", %s=\"%s\"", k, v)
+		}
+		_, _ = fmt.Fprintf(&b, "];\n")
 	}
 
 	b.WriteString("\n")
 
 	for _, e := range edges {
-		_, _ = fmt.Fprintf(&b, "\tnode%d -> node%d;\n", e.from, e.to)
+		_, _ = fmt.Fprintf(&b, "\tnode%d:f%d -> node%d;\n", e.from, e.childIdx, e.to)
 	}
 
 	b.WriteString("}")
diff --git a/unmarshaler.go b/unmarshaler.go
index 1fee384..45f8fbc 100644
--- a/unmarshaler.go
+++ b/unmarshaler.go
@@ -2,6 +2,7 @@ package toml
 
 import (
 	"fmt"
+	"os"
 	"reflect"
 
 	"github.com/pelletier/go-toml/v2/internal/ast"
@@ -13,9 +14,28 @@ func Unmarshal(data []byte, v interface{}) error {
 	if err != nil {
 		return err
 	}
+
+	// TODO: remove me; sanity check
+	allValidOrDump(p.tree, p.tree)
+
 	return fromAst(p.tree, v)
 }
 
+func allValidOrDump(tree ast.Root, nodes []ast.Node) bool {
+	for i, n := range nodes {
+		if n.Kind == ast.Invalid {
+			fmt.Printf("AST contains invalid node! idx=%d\n", i)
+			fmt.Fprintf(os.Stderr, "%s\n", tree.Sdot())
+			return false
+		}
+		ok := allValidOrDump(tree, n.Children)
+		if !ok {
+			return ok
+		}
+	}
+	return true
+}
+
 func fromAst(tree ast.Root, v interface{}) error {
 	r := reflect.ValueOf(v)
 	if r.Kind() != reflect.Ptr {