diff --git a/internal/core/export/export_test.go b/internal/core/export/export_test.go
index 5e7071301..379520156 100644
--- a/internal/core/export/export_test.go
+++ b/internal/core/export/export_test.go
@@ -377,3 +377,24 @@ func TestFromAPI(t *testing.T) {
 		})
 	}
 }
+
+// TestNoPanicCyclicBuiltinValidator is a regression test for a stack overflow
+// in vertex() when a BuiltinValidator argument contains a vertex that is
+// already on the export stack. For example, exporting
+//
+//	#c: { a?: matchN(1, [#c]) }
+//
+// caused infinite recursion: vertex(#c) → structComposite → vertex(a) →
+// builtinValidator → value([#c]) → vertex(#c) → …
+func TestNoPanicCyclicBuiltinValidator(t *testing.T) {
+	cuetdtest.FullMatrix.Run(t, "", func(t *testing.T, m *cuetdtest.M) {
+		ctx := m.CueContext()
+		v := ctx.CompileString(`#c: { a?: matchN(1, [#c]) }`)
+		if err := v.Err(); err != nil {
+			t.Fatal(err)
+		}
+		r, x := value.ToInternal(v)
+		// Must complete without stack overflow.
+		_, _ = export.Def(r, "", x)
+	})
+}
diff --git a/internal/core/export/value.go b/internal/core/export/value.go
index 352d5b57a..883d52144 100644
--- a/internal/core/export/value.go
+++ b/internal/core/export/value.go
@@ -44,6 +44,14 @@ func (e *exporter) bareValue(v adt.Value) ast.Expr {
 // value with a reference in graph mode.
 
 func (e *exporter) vertex(n *adt.Vertex) (result ast.Expr) {
+	// Guard against infinite recursion when a vertex cycles back to itself
+	// through BuiltinValidator arguments or other value-level cycles.
+	for i := range e.stack {
+		if e.stack[i].node == n {
+			return ast.NewIdent("_")
+		}
+	}
+
 	var attrs []*ast.Attribute
 	if e.cfg.ShowAttributes {
 		attrs = ExtractDeclAttrs(n)