diff --git a/packages/svelte/src/compiler/types/template.d.ts b/packages/svelte/src/compiler/types/template.d.ts
index 08d348fb2f..c2c79f2b57 100644
--- a/packages/svelte/src/compiler/types/template.d.ts
+++ b/packages/svelte/src/compiler/types/template.d.ts
@@ -88,7 +88,7 @@ export namespace AST {
 		customRenderer?: string;
 		customElement?: {
 			tag?: string;
-			shadow?: 'open' | 'none';
+			shadow?: 'open' | 'none' | ObjectExpression | undefined;
 			props?: Record<
 				string,
 				{
diff --git a/packages/svelte/types/index.d.ts b/packages/svelte/types/index.d.ts
index fecbcda419..741c2babc2 100644
--- a/packages/svelte/types/index.d.ts
+++ b/packages/svelte/types/index.d.ts
@@ -1251,7 +1251,7 @@ declare module 'svelte/compiler' {
 			customRenderer?: string;
 			customElement?: {
 				tag?: string;
-				shadow?: 'open' | 'none';
+				shadow?: 'open' | 'none' | ObjectExpression | undefined;
 				props?: Record<
 					string,
 					{