diff --git a/packages/svelte/src/internal/client/hydratable.js b/packages/svelte/src/internal/client/hydratable.js
index 9628bdb1dd..780bbed37c 100644
--- a/packages/svelte/src/internal/client/hydratable.js
+++ b/packages/svelte/src/internal/client/hydratable.js
@@ -1,4 +1,4 @@
-/** @import { Parse, Transport } from '#shared' */
+/** @import { Decode, Transport } from '#shared' */
 import { hydrating } from './dom/hydration.js';
 
 /**
@@ -19,13 +19,13 @@ export function hydratable(key, fn, options = {}) {
 		// something to be synchronously hydratable and then have it not be
 		return fn();
 	}
-	return parse(val, options.transport?.parse);
+	return parse(val, options.transport?.decode);
 }
 
 /**
  * @template T
  * @param {string} key
- * @param {{ parse?: Parse<T> }} [options]
+ * @param {{ parse?: Decode<T> }} [options]
  * @returns {T | undefined}
  */
 export function get_hydratable_value(key, options = {}) {
@@ -57,10 +57,10 @@ export function has_hydratable_value(key) {
 
 /**
  * @template T
- * @param {string} val
- * @param {Parse<T> | undefined} parse
+ * @param {unknown} val
+ * @param {Decode<T> | undefined} parse
  * @returns {T}
  */
 function parse(val, parse) {
-	return (parse ?? ((val) => new Function(`return (${val})`)()))(val);
+	return (parse ?? ((val) => /** @type {T} */ (val)))(val);
 }
diff --git a/packages/svelte/src/internal/server/hydratable.js b/packages/svelte/src/internal/server/hydratable.js
index d538cfdb32..2d6600a7ae 100644
--- a/packages/svelte/src/internal/server/hydratable.js
+++ b/packages/svelte/src/internal/server/hydratable.js
@@ -1,4 +1,4 @@
-/** @import { Stringify, Transport } from '#shared' */
+/** @import { Encode, Transport } from '#shared' */
 
 import { get_render_context } from './render-context.js';
 
@@ -26,14 +26,14 @@ export function hydratable(key, fn, options = {}) {
 	}
 
 	const result = fn();
-	store.hydratables.set(key, { value: result, stringify: options.transport?.stringify });
+	store.hydratables.set(key, { value: result, encode: options.transport?.encode });
 	return result;
 }
 /**
  * @template T
  * @param {string} key
  * @param {T} value
- * @param {{ stringify?: Stringify<T> }} [options]
+ * @param {{ encode?: Encode<T> }} [options]
  */
 export function set_hydratable_value(key, value, options = {}) {
 	const store = get_render_context();
@@ -45,6 +45,6 @@ export function set_hydratable_value(key, value, options = {}) {
 
 	store.hydratables.set(key, {
 		value,
-		stringify: options.stringify
+		encode: options.encode
 	});
 }
diff --git a/packages/svelte/src/internal/server/renderer.js b/packages/svelte/src/internal/server/renderer.js
index d4360635c0..5cccbc602b 100644
--- a/packages/svelte/src/internal/server/renderer.js
+++ b/packages/svelte/src/internal/server/renderer.js
@@ -578,15 +578,15 @@ export class Renderer {
 		/** @type {(value: unknown) => string} */
 		let default_stringify;
 
-		/** @type {[string, string][]} */
+		/** @type {[string, unknown][]} */
 		let entries = [];
 		for (const [k, v] of map) {
-			const serialize = v.stringify ?? (default_stringify ??= uneval);
+			const encode = v.encode ?? (default_stringify ??= new MemoizedUneval().uneval);
 			// sequential await is okay here -- all the work is already kicked off
-			entries.push([k, serialize(await v.value)]);
+			entries.push([k, encode(await v.value)]);
 		}
 		if (entries.length === 0) return null;
-		return Renderer.#hydratable_block(JSON.stringify(entries));
+		return Renderer.#hydratable_block(entries);
 	}
 
 	/**
@@ -643,23 +643,20 @@ export class Renderer {
 		};
 	}
 
-	/** @param {string} serialized */
+	/** @param {[string, unknown][]} serialized */
 	static #hydratable_block(serialized) {
+		let entries = '';
+		for (const [k, v] of serialized) {
+			entries += `["${k}",${v}],`;
+		}
 		// TODO csp?
 		// TODO how can we communicate this error better? Is there a way to not just send it to the console?
 		// (it is probably very rare so... not too worried)
 		return `
 <script>
 	var store = (window.__svelte ??= {}).h ??= new Map();
-	for (const [k,v] of ${serialized}) {
-		if (!store.has(k)) {
+	for (const [k,v] of ${entries}) {
 			store.set(k, v);
-			continue;
-		}
-		var stored_val = store.get(k);
-		if (stored_val.value !== v) {
-			throw new Error('TODO tried to populate the same hydratable key twice with different values');
-		}
 	}
 </script>`;
 	}
diff --git a/packages/svelte/src/internal/server/types.d.ts b/packages/svelte/src/internal/server/types.d.ts
index 8eea679069..2cdf2df277 100644
--- a/packages/svelte/src/internal/server/types.d.ts
+++ b/packages/svelte/src/internal/server/types.d.ts
@@ -1,4 +1,4 @@
-import type { CacheEntry, Stringify } from '#shared';
+import type { CacheEntry, Encode } from '#shared';
 import type { Element } from './dev';
 import type { Renderer } from './renderer';
 
@@ -20,7 +20,7 @@ export interface RenderContext {
 		string,
 		{
 			value: unknown;
-			stringify: Stringify<any> | undefined;
+			encode: Encode<any> | undefined;
 		}
 	>;
 	cache: Map<string, CacheEntry>;
diff --git a/packages/svelte/src/internal/shared/types.d.ts b/packages/svelte/src/internal/shared/types.d.ts
index f5e3665db6..89cb28f6ec 100644
--- a/packages/svelte/src/internal/shared/types.d.ts
+++ b/packages/svelte/src/internal/shared/types.d.ts
@@ -11,18 +11,18 @@ export type Snapshot<T> = ReturnType<typeof $state.snapshot<T>>;
 
 export type MaybePromise<T> = T | Promise<T>;
 
-export type Parse<T> = (value: string) => T;
+export type Decode<T> = (value: unknown) => T;
 
-export type Stringify<T> = (value: T) => string;
+export type Encode<T> = (value: T) => unknown;
 
 export type Transport<T> =
 	| {
-			stringify: Stringify<T>;
-			parse?: undefined;
+			encode: Encode<T>;
+			decode?: undefined;
 	  }
 	| {
-			stringify?: undefined;
-			parse: Parse<T>;
+			encode?: undefined;
+			decode: Decode<T>;
 	  };
 
 export type Resource<T> = {
diff --git a/packages/svelte/types/index.d.ts b/packages/svelte/types/index.d.ts
index 5e000126bb..72ec09567e 100644
--- a/packages/svelte/types/index.d.ts
+++ b/packages/svelte/types/index.d.ts
@@ -598,18 +598,18 @@ declare module 'svelte' {
 		[K in keyof T]: () => T[K];
 	};
 
-	type Parse<T> = (value: string) => T;
+	type Decode<T> = (value: unknown) => T;
 
-	type Stringify<T> = (value: T) => string;
+	type Encode<T> = (value: T) => unknown;
 
 	type Transport<T> =
 		| {
-				stringify: Stringify<T>;
-				parse?: undefined;
+				encode: Encode<T>;
+				decode?: undefined;
 		  }
 		| {
-				stringify?: undefined;
-				parse: Parse<T>;
+				encode?: undefined;
+				decode: Decode<T>;
 		  };
 
 	export {};
@@ -2613,20 +2613,20 @@ declare module 'svelte/server' {
 
 	type RenderOutput = SyncRenderOutput & PromiseLike<SyncRenderOutput>;
 	export function setHydratableValue<T>(key: string, value: T, options?: {
-		stringify?: Stringify<T>;
+		encode?: Encode<T>;
 	} | undefined): void;
-	type Stringify<T> = (value: T) => string;
+	type Encode<T> = (value: T) => unknown;
 
 	export {};
 }
 
 declare module 'svelte/client' {
 	export function getHydratableValue<T>(key: string, options?: {
-		parse?: Parse<T>;
+		parse?: Decode<T>;
 	} | undefined): T | undefined;
 
 	export function hasHydratableValue(key: string): boolean;
-	type Parse<T> = (value: string) => T;
+	type Decode<T> = (value: unknown) => T;
 
 	export {};
 }