diff --git a/documentation/docs/98-reference/.generated/compile-errors.md b/documentation/docs/98-reference/.generated/compile-errors.md
index 20f57770d122..957a9f67c7b0 100644
--- a/documentation/docs/98-reference/.generated/compile-errors.md
+++ b/documentation/docs/98-reference/.generated/compile-errors.md
@@ -364,6 +364,12 @@ The $ name is reserved, and cannot be used for variables and imports
 The $ prefix is reserved, and cannot be used for variables and imports
 ```
 
+### duplicate_class_field
+
+```
+`%name%` has already been declared
+```
+
 ### each_item_invalid_assignment
 
 ```
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index 450ecde53b1e..766c83763acc 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,13 @@
 # svelte
 
+## 5.36.17
+
+### Patch Changes
+
+- fix: throw on duplicate class field declarations ([#16502](https://github.com/sveltejs/svelte/pull/16502))
+
+- fix: add types for `part` attribute to svg attributes ([#16499](https://github.com/sveltejs/svelte/pull/16499))
+
 ## 5.36.16
 
 ### Patch Changes
diff --git a/packages/svelte/elements.d.ts b/packages/svelte/elements.d.ts
index 604241592aff..2e1042dfd6b8 100644
--- a/packages/svelte/elements.d.ts
+++ b/packages/svelte/elements.d.ts
@@ -1553,6 +1553,7 @@ export interface SVGAttributes<T extends EventTarget> extends AriaAttributes, DO
 	height?: number | string | undefined | null;
 	id?: string | undefined | null;
 	lang?: string | undefined | null;
+	part?: string | undefined | null;
 	max?: number | string | undefined | null;
 	media?: string | undefined | null;
 	// On the `textPath` element
diff --git a/packages/svelte/messages/compile-errors/script.md b/packages/svelte/messages/compile-errors/script.md
index 2b0c5eafdf86..5c1080acedfe 100644
--- a/packages/svelte/messages/compile-errors/script.md
+++ b/packages/svelte/messages/compile-errors/script.md
@@ -30,6 +30,10 @@
 
 > The $ prefix is reserved, and cannot be used for variables and imports
 
+## duplicate_class_field
+
+> `%name%` has already been declared
+
 ## each_item_invalid_assignment
 
 > Cannot reassign or bind to each block argument in runes mode. Use the array and index variables instead (e.g. `array[i] = value` instead of `entry = value`, or `bind:value={array[i]}` instead of `bind:value={entry}`)
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 07954026b550..22bc8cc8fac6 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.36.16",
+  "version": "5.36.17",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/compiler/errors.js b/packages/svelte/src/compiler/errors.js
index 599d3e8248b0..e763a6e0733a 100644
--- a/packages/svelte/src/compiler/errors.js
+++ b/packages/svelte/src/compiler/errors.js
@@ -152,6 +152,16 @@ export function dollar_prefix_invalid(node) {
 	e(node, 'dollar_prefix_invalid', `The $ prefix is reserved, and cannot be used for variables and imports\nhttps://svelte.dev/e/dollar_prefix_invalid`);
 }
 
+/**
+ * `%name%` has already been declared
+ * @param {null | number | NodeLike} node
+ * @param {string} name
+ * @returns {never}
+ */
+export function duplicate_class_field(node, name) {
+	e(node, 'duplicate_class_field', `\`${name}\` has already been declared\nhttps://svelte.dev/e/duplicate_class_field`);
+}
+
 /**
  * Cannot reassign or bind to each block argument in runes mode. Use the array and index variables instead (e.g. `array[i] = value` instead of `entry = value`, or `bind:value={array[i]}` instead of `bind:value={entry}`)
  * @param {null | number | NodeLike} node
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/ClassBody.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/ClassBody.js
index ffc39ac00de1..2bfc1dbce36c 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/ClassBody.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/ClassBody.js
@@ -33,6 +33,9 @@ export function ClassBody(node, context) {
 	/** @type {Map<string, StateField>} */
 	const state_fields = new Map();
 
+	/** @type {Map<string, Array<MethodDefinition['kind'] | 'prop' | 'assigned_prop'>>} */
+	const fields = new Map();
+
 	context.state.analysis.classes.set(node, state_fields);
 
 	/** @type {MethodDefinition | null} */
@@ -54,6 +57,14 @@ export function ClassBody(node, context) {
 				e.state_field_duplicate(node, name);
 			}
 
+			const _key = (key.type === 'PrivateIdentifier' ? '#' : '') + name;
+			const field = fields.get(_key);
+
+			// if there's already a method or assigned field, error
+			if (field && !(field.length === 1 && field[0] === 'prop')) {
+				e.duplicate_class_field(node, _key);
+			}
+
 			state_fields.set(name, {
 				node,
 				type: rune,
@@ -67,10 +78,48 @@ export function ClassBody(node, context) {
 	for (const child of node.body) {
 		if (child.type === 'PropertyDefinition' && !child.computed && !child.static) {
 			handle(child, child.key, child.value);
+			const key = (child.key.type === 'PrivateIdentifier' ? '#' : '') + get_name(child.key);
+			const field = fields.get(key);
+			if (!field) {
+				fields.set(key, [child.value ? 'assigned_prop' : 'prop']);
+				continue;
+			}
+			e.duplicate_class_field(child, key);
 		}
 
-		if (child.type === 'MethodDefinition' && child.kind === 'constructor') {
-			constructor = child;
+		if (child.type === 'MethodDefinition') {
+			if (child.kind === 'constructor') {
+				constructor = child;
+			} else if (!child.computed) {
+				const key = (child.key.type === 'PrivateIdentifier' ? '#' : '') + get_name(child.key);
+				const field = fields.get(key);
+				if (!field) {
+					fields.set(key, [child.kind]);
+					continue;
+				}
+				if (
+					field.includes(child.kind) ||
+					field.includes('prop') ||
+					field.includes('assigned_prop')
+				) {
+					e.duplicate_class_field(child, key);
+				}
+				if (child.kind === 'get') {
+					if (field.length === 1 && field[0] === 'set') {
+						field.push('get');
+						continue;
+					}
+				} else if (child.kind === 'set') {
+					if (field.length === 1 && field[0] === 'get') {
+						field.push('set');
+						continue;
+					}
+				} else {
+					field.push(child.kind);
+					continue;
+				}
+				e.duplicate_class_field(child, key);
+			}
 		}
 	}
 
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index 5d76fc3f2963..d2992a3dcd8c 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.36.16';
+export const VERSION = '5.36.17';
 export const PUBLIC_VERSION = '5';
diff --git a/packages/svelte/tests/validator/samples/class-state-constructor-9/errors.json b/packages/svelte/tests/validator/samples/class-state-constructor-9/errors.json
index b7dd4c8ed457..94b5f191c2f7 100644
--- a/packages/svelte/tests/validator/samples/class-state-constructor-9/errors.json
+++ b/packages/svelte/tests/validator/samples/class-state-constructor-9/errors.json
@@ -1,14 +1,14 @@
 [
 	{
-		"code": "state_field_invalid_assignment",
-		"message": "Cannot assign to a state field before its declaration",
+		"code": "duplicate_class_field",
+		"message": "`count` has already been declared",
 		"start": {
-			"line": 2,
-			"column": 1
+			"line": 5,
+			"column": 2
 		},
 		"end": {
-			"line": 2,
-			"column": 12
+			"line": 5,
+			"column": 24
 		}
 	}
 ]

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