diff --git a/ast/ast.go b/ast/ast.go
index 66059e9..0f3d3e6 100644
--- a/ast/ast.go
+++ b/ast/ast.go
@@ -26,7 +26,10 @@ const (
 type NodeKind int
 
 func (k NodeKind) String() string {
-	return kindNames[k]
+	if int(k) < len(kindNames) {
+		return kindNames[k]
+	}
+	return fmt.Sprintf("NodeKind(%v)", int(k))
 }
 
 var kindMax NodeKind
diff --git a/ast/ast_test.go b/ast/ast_test.go
index 684fbc3..0a54c5d 100644
--- a/ast/ast_test.go
+++ b/ast/ast_test.go
@@ -73,3 +73,31 @@ func node(n Node, children ...Node) Node {
 	}
 	return n
 }
+
+func TestNodeKindString(t *testing.T) {
+	tests := []struct {
+		name string
+		give NodeKind
+		want string
+	}{
+		{
+			name: "known",
+			give: KindLink,
+			want: "Link",
+		},
+		{
+			name: "unknown",
+			give: NodeKind(500),
+			want: "NodeKind(500)",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := tt.give.String()
+			if tt.want != got {
+				t.Errorf("String() expected %q, got %q", tt.want, got)
+			}
+		})
+	}
+}