diff --git a/.changeset/eight-pianos-raise.md b/.changeset/eight-pianos-raise.md
new file mode 100644
index 0000000000..d73c7424a9
--- /dev/null
+++ b/.changeset/eight-pianos-raise.md
@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: add backwards-compat for old warning codes in legacy mode
diff --git a/packages/svelte/src/compiler/migrate/index.js b/packages/svelte/src/compiler/migrate/index.js
index 6f5d2681d9..7d5ca36599 100644
--- a/packages/svelte/src/compiler/migrate/index.js
+++ b/packages/svelte/src/compiler/migrate/index.js
@@ -7,6 +7,7 @@ import { get_rune } from '../phases/scope.js';
 import { reset } from '../state.js';
 import { extract_identifiers } from '../utils/ast.js';
 import { regex_is_valid_identifier } from '../phases/patterns.js';
+import { migrate_svelte_ignore } from '../utils/extract_svelte_ignore.js';
 
 /**
  * Does a best-effort migration of Svelte code towards using runes, event attributes and render tags.
@@ -174,6 +175,21 @@ export function migrate(source) {
 
 /** @type {import('zimmerframe').Visitors<import('../types/template.js').SvelteNode, State>} */
 const instance_script = {
+	_(node, { state, next }) {
+		// @ts-expect-error
+		const comments = node.leadingComments;
+		if (comments) {
+			for (const comment of comments) {
+				if (comment.type === 'Line') {
+					const migrated = migrate_svelte_ignore(comment.value);
+					if (migrated !== comment.value) {
+						state.str.overwrite(comment.start + '//'.length, comment.end, migrated);
+					}
+				}
+			}
+		}
+		next();
+	},
 	Identifier(node, { state }) {
 		handle_identifier(node, state);
 	},
@@ -474,6 +490,12 @@ const template = {
 		} else {
 			state.str.update(node.start, node.end, `{@render ${name}?.(${slot_props})}`);
 		}
+	},
+	Comment(node, { state }) {
+		const migrated = migrate_svelte_ignore(node.data);
+		if (migrated !== node.data) {
+			state.str.overwrite(node.start + '<!--'.length, node.end - '-->'.length, migrated);
+		}
 	}
 };
 
diff --git a/packages/svelte/src/compiler/utils/extract_svelte_ignore.js b/packages/svelte/src/compiler/utils/extract_svelte_ignore.js
index d68a9515fc..1f5d29db7d 100644
--- a/packages/svelte/src/compiler/utils/extract_svelte_ignore.js
+++ b/packages/svelte/src/compiler/utils/extract_svelte_ignore.js
@@ -3,9 +3,16 @@ import * as w from '../warnings.js';
 
 const regex_svelte_ignore = /^\s*svelte-ignore\s/;
 
-/** @type {Record<string, string>} */
+/** @type {Record<string, string>} Map of legacy code -> new code */
 const replacements = {
-	'non-top-level-reactive-declaration': 'reactive_declaration_invalid_placement'
+	'non-top-level-reactive-declaration': 'reactive_declaration_invalid_placement',
+	'module-script-reactive-declaration': 'reactive_declaration_module_script',
+	'empty-block': 'block_empty',
+	'avoid-is': 'attribute_avoid_is',
+	'invalid-html-attribute': 'attribute_invalid_property_name',
+	'a11y-structure': 'a11y_figcaption_parent',
+	'illegal-attribute-character': 'attribute_illegal_colon',
+	'invalid-rest-eachblock-binding': 'bind_invalid_each_rest'
 };
 
 /**
@@ -56,3 +63,21 @@ export function extract_svelte_ignore(offset, text, runes) {
 
 	return ignores;
 }
+
+/**
+ * Replaces legacy svelte-ignore codes with new codes.
+ * @param {string} text
+ * @returns {string}
+ */
+export function migrate_svelte_ignore(text) {
+	const match = regex_svelte_ignore.exec(text);
+	if (!match) return text;
+
+	const length = match[0].length;
+	return (
+		text.substring(0, length) +
+		text
+			.substring(length)
+			.replace(/\w+-\w+(-\w+)*/g, (code) => replacements[code] ?? code.replace(/-/g, '_'))
+	);
+}
diff --git a/packages/svelte/tests/migrate/samples/svelte-ignore/input.svelte b/packages/svelte/tests/migrate/samples/svelte-ignore/input.svelte
new file mode 100644
index 0000000000..fa734942f9
--- /dev/null
+++ b/packages/svelte/tests/migrate/samples/svelte-ignore/input.svelte
@@ -0,0 +1,9 @@
+<script>
+	function foo() {
+		// svelte-ignore non-top-level-reactive-declaration
+		$: x = 1;
+	}
+</script>
+
+<!-- svelte-ignore a11y-something-something -->
+<div></div>
\ No newline at end of file
diff --git a/packages/svelte/tests/migrate/samples/svelte-ignore/output.svelte b/packages/svelte/tests/migrate/samples/svelte-ignore/output.svelte
new file mode 100644
index 0000000000..fa305cefb1
--- /dev/null
+++ b/packages/svelte/tests/migrate/samples/svelte-ignore/output.svelte
@@ -0,0 +1,9 @@
+<script>
+	function foo() {
+		// svelte-ignore reactive_declaration_invalid_placement
+		$: x = 1;
+	}
+</script>
+
+<!-- svelte-ignore a11y_something_something -->
+<div></div>
\ No newline at end of file