diff --git a/packages/svelte/src/internal/server/hydratable.js b/packages/svelte/src/internal/server/hydratable.js
index ba081972e7..8bdb6ca15d 100644
--- a/packages/svelte/src/internal/server/hydratable.js
+++ b/packages/svelte/src/internal/server/hydratable.js
@@ -59,7 +59,12 @@ function encode(key, value, values, unresolved) {
 			serialize_promise.finally(() => unresolved?.delete(serialize_promise));
 
 			const index = values.push(serialize_promise) - 1;
-			const result = `d(${index})`;
+
+			// in dev, we serialize promises as `d("1")` instead of `d(1)`, because it's
+			// impossible for that string to occur 'naturally' (since the quote marks
+			// would have to be escaped). this allows us to check that repeat occurrences
+			// of a given hydratable are identical with a simple string comparison
+			const result = DEV ? `d("${index}")` : `d(${index})`;
 
 			if (DEV) {
 				(entry.promises ??= []).push(
diff --git a/packages/svelte/src/internal/server/renderer.js b/packages/svelte/src/internal/server/renderer.js
index 761b1415b0..601494aa47 100644
--- a/packages/svelte/src/internal/server/renderer.js
+++ b/packages/svelte/src/internal/server/renderer.js
@@ -654,7 +654,12 @@ export class Renderer {
 			return null;
 		}
 
-		const values = await Promise.all(ctx.values);
+		let values = await Promise.all(ctx.values);
+
+		if (DEV) {
+			// turn `d("1")` into `d(1)` — see `hydratable.js` for an explanation
+			values = values.map((v) => v.replace(/d\("(\d+)"\)/g, (_, i) => `d(${i})`));
+		}
 
 		// TODO csp -- have discussed but not implemented
 		return `