diff --git a/.changeset/cuddly-cougars-grow.md b/.changeset/cuddly-cougars-grow.md
new file mode 100644
index 0000000000..a319be9775
--- /dev/null
+++ b/.changeset/cuddly-cougars-grow.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: strip trailing semicolons in style directive reactive updates
diff --git a/packages/svelte/src/internal/client/dom/elements/style.js b/packages/svelte/src/internal/client/dom/elements/style.js
index 740c225f29..91a3c7a261 100644
--- a/packages/svelte/src/internal/client/dom/elements/style.js
+++ b/packages/svelte/src/internal/client/dom/elements/style.js
@@ -1,3 +1,4 @@
+import { DEV } from 'esm-env';
 import { to_style } from '../../../shared/attributes.js';
 import { STYLE_CACHE } from '../../constants.js';
 import { hydrating } from '../hydration.js';
@@ -13,10 +14,21 @@ function update_styles(dom, prev = {}, next, priority) {
 		var value = next[key];
 
 		if (prev[key] !== value) {
-			if (next[key] == null) {
+			if (value == null) {
 				dom.style.removeProperty(key);
 			} else {
-				dom.style.setProperty(key, value, priority);
+				var str_value = String(value);
+
+				if (DEV && /;+\s*$/.test(str_value)) {
+					// eslint-disable-next-line no-console
+					console.warn(
+						`[svelte] Style directive value for "${key}" has a trailing semicolon which is invalid and will be removed. Remove the trailing ";" from the value.`
+					);
+				}
+
+				// setProperty rejects values with trailing semicolons; strip them so that
+				// reactive updates behave consistently with the initial cssText assignment
+				dom.style.setProperty(key, str_value.replace(/;+\s*$/, ''), priority);
 			}
 		}
 	}
diff --git a/packages/svelte/tests/runtime-browser/samples/style-directive-trailing-semicolon/_config.js b/packages/svelte/tests/runtime-browser/samples/style-directive-trailing-semicolon/_config.js
new file mode 100644
index 0000000000..1e96ec17f7
--- /dev/null
+++ b/packages/svelte/tests/runtime-browser/samples/style-directive-trailing-semicolon/_config.js
@@ -0,0 +1,21 @@
+import { assert_ok, test } from '../../assert';
+
+export default test({
+	html: `<div style="color: red;"></div>`,
+
+	test({ assert, target, window, component }) {
+		const div = target.querySelector('div');
+		assert_ok(div);
+
+		// Initial value with trailing semicolon — should produce valid CSS
+		assert.equal(window.getComputedStyle(div).color, 'rgb(255, 0, 0)');
+
+		// Update to a new value that also has a trailing semicolon
+		component.color = 'blue;';
+		assert.equal(window.getComputedStyle(div).color, 'rgb(0, 0, 255)');
+
+		// Update to a value without trailing semicolon — should still work
+		component.color = 'green';
+		assert.equal(window.getComputedStyle(div).color, 'rgb(0, 128, 0)');
+	}
+});
diff --git a/packages/svelte/tests/runtime-browser/samples/style-directive-trailing-semicolon/main.svelte b/packages/svelte/tests/runtime-browser/samples/style-directive-trailing-semicolon/main.svelte
new file mode 100644
index 0000000000..3ba2e22bc0
--- /dev/null
+++ b/packages/svelte/tests/runtime-browser/samples/style-directive-trailing-semicolon/main.svelte
@@ -0,0 +1,5 @@
+<script lang="ts">
+	export let color = 'red;';
+</script>
+
+<div style:color={color}></div>