diff --git a/src/morphlex.ts b/src/morphlex.ts
index 4b55a30..07452d0 100644
--- a/src/morphlex.ts
+++ b/src/morphlex.ts
@@ -385,6 +385,7 @@ class Morph {
 
 		// First pass: update/add attributes from reference (iterate forwards)
 		for (const { name, value } of to.attributes) {
+			if (name === "morphlex-dirty") continue
 			if (name === "value") {
 				if (isInputElement(from) && from.type !== "file" && from.value !== value) {
 					if (!this.#options.preserveChanges) {
diff --git a/test/new/dirty-attribute-injection.browser.test.ts b/test/new/dirty-attribute-injection.browser.test.ts
new file mode 100644
index 0000000..9b3e634
--- /dev/null
+++ b/test/new/dirty-attribute-injection.browser.test.ts
@@ -0,0 +1,16 @@
+import { expect, test } from "vitest"
+import { morph } from "../../src/morphlex"
+
+test("morphlex-dirty attribute in `to` does not leak into `from`", () => {
+	const from = document.createElement("div")
+	from.id = "x"
+
+	// Hostile/buggy input includes morphlex-dirty on the target.
+	const to = document.createElement("div")
+	to.id = "x"
+	to.setAttribute("morphlex-dirty", "")
+
+	morph(from, to)
+
+	expect(from.hasAttribute("morphlex-dirty")).toBe(false)
+})