diff --git a/README.md b/README.md
index b59947fc..45c8b7d4 100644
--- a/README.md
+++ b/README.md
@@ -73,6 +73,11 @@ If you have a question, or hit a problem, feel free to ask on our [gitter channe
 
 Or, if you encounter a bug, something is unclear in the code or documentation, don’t hesitate and open an issue on GitHub.
 
+### Testing Scala.js
+
+Scala.js tests require [chromedriver](https://chromedriver.chromium.org/). It is downloaded automatically
+by the `test` task. Make sure to run it before running tests in any other way, e.g. using `testOnly`.
+
 ### Building & testing the scala-native version
 
 By default, sttp-native will **not** be included in the aggregate build of the root project. To include it, define the `STTP_NATIVE` environmental variable before running sbt, e.g.:
diff --git a/core/src/main/scala/sttp/model/Part.scala b/core/src/main/scala/sttp/model/Part.scala
index ebb5341d..46159af8 100644
--- a/core/src/main/scala/sttp/model/Part.scala
+++ b/core/src/main/scala/sttp/model/Part.scala
@@ -41,9 +41,30 @@ case class Part[+T](
   // enumerate all variants so that overload resolution works correctly
   override def header(h: String): Option[String] = super.header(h)
 
+  /**
+   * Returns the value of the `Content-Disposition` header, which should be used when sending this part in a
+   * multipart request.
+   *
+   * The syntax is specified by [[https://datatracker.ietf.org/doc/html/rfc6266#section-4.1 RFC6266 section 4.1]].
+   * For safety and simplicity, disposition parameter values are represented as `quoted-string`, defined in
+   * [[https://datatracker.ietf.org/doc/html/rfc9110#section-5.6.4 RFC9110 section 5.6.4]].
+   *
+   * `quoted-string` allows usage of visible ASCII characters (`%x21-7E`), except for `"` and `\`, which must be escaped
+   * with a backslash. Additionally, space and horizontal tab is allowed, as well as octets `0x80-FF` (`obs-data`).
+   * In practice this means that - while not explicitly allowed - non-ASCII UTF-8 characters are valid
+   * according to this grammar. Additionally, [[https://datatracker.ietf.org/doc/html/rfc6532#section-3.2 RFC6532]]
+   * makes it more explicit that non-ASCII UTF-8 is allowed. Control characters are not allowed.
+   *
+   * This method makes sure that `"` and `\` are escaped, while leaving possible rejection of forbidden characters to
+   * lower layers (`sttp` backends).
+   */
   def contentDispositionHeaderValue: String = {
-    def encode(s: String): String = new String(s.getBytes("utf-8"), "iso-8859-1")
-    "form-data; " + dispositionParamsSeq.map { case (k, v) => s"""$k="${encode(v)}"""" }.mkString("; ")
+    def escape(str: String): String = str.flatMap {
+      case '"' => "\\\""
+      case '\\' => "\\\\"
+      case c => c.toString
+    }
+    "form-data; " + dispositionParamsSeq.map { case (k, v) => s"""$k="${escape(v)}"""" }.mkString("; ")
   }
 
   def dispositionParams: Map[String, String] = dispositionParamsSeq.toMap
diff --git a/core/src/test/scala/sttp/model/PartTest.scala b/core/src/test/scala/sttp/model/PartTest.scala
new file mode 100644
index 00000000..e4faad99
--- /dev/null
+++ b/core/src/test/scala/sttp/model/PartTest.scala
@@ -0,0 +1,21 @@
+package sttp.model
+
+import org.scalatest.flatspec.AnyFlatSpec
+import org.scalatest.matchers.should.Matchers
+
+class PartTest extends AnyFlatSpec with Matchers {
+  it should "encode content-disposition header correctly" in {
+    val part = Part("name", 42).fileName("f1.txt")
+    part.contentDispositionHeaderValue shouldBe """form-data; name="name"; filename="f1.txt""""
+  }
+
+  it should "retain non-ascii characters in filename" in {
+    val part = Part("name", 42).fileName("fó1.txt")
+    part.contentDispositionHeaderValue shouldBe """form-data; name="name"; filename="fó1.txt""""
+  }
+
+  it should "escape double quote and backslash in filename" in {
+    val part = Part("name", 42).fileName("f\"\\1.txt")
+    part.contentDispositionHeaderValue shouldBe """form-data; name="name"; filename="f\"\\1.txt""""
+  }
+}