diff --git a/components/script/dom/xmlhttprequest.rs b/components/script/dom/xmlhttprequest.rs
index 86131fa502f..22f0ba46a1a 100644
--- a/components/script/dom/xmlhttprequest.rs
+++ b/components/script/dom/xmlhttprequest.rs
@@ -739,7 +739,7 @@ impl XMLHttpRequestMethods<crate::DomTypeHolder> for XMLHttpRequest {
                                     .collect();
 
                                 let new_mime = format!(
-                                    "{}/{}; charset={}{}{}",
+                                    "{}/{};charset={}{}{}",
                                     mime.type_,
                                     mime.subtype,
                                     encoding,
@@ -750,9 +750,11 @@ impl XMLHttpRequestMethods<crate::DomTypeHolder> for XMLHttpRequest {
                                         .collect::<Vec<String>>()
                                         .join("; ")
                                 );
-                                request
-                                    .headers
-                                    .typed_insert(ContentType::from_str(&new_mime).unwrap())
+
+                                request.headers.insert(
+                                    header::CONTENT_TYPE,
+                                    HeaderValue::from_str(&new_mime).unwrap(),
+                                );
                             }
                         }
                     }
diff --git a/tests/wpt/meta/MANIFEST.json b/tests/wpt/meta/MANIFEST.json
index 94665de8238..ab585890587 100644
--- a/tests/wpt/meta/MANIFEST.json
+++ b/tests/wpt/meta/MANIFEST.json
@@ -922538,7 +922538,7 @@
      ]
     ],
     "setrequestheader-content-type.htm": [
-     "07238391eb5cc8639edbe996208a18b6d9d26b04",
+     "c78482142469cf966c3f64287c81c78bcd4f3e63",
      [
       null,
       {
diff --git a/tests/wpt/meta/xhr/send-content-type-charset.htm.ini b/tests/wpt/meta/xhr/send-content-type-charset.htm.ini
index b30fab0e927..3e3e615dc1c 100644
--- a/tests/wpt/meta/xhr/send-content-type-charset.htm.ini
+++ b/tests/wpt/meta/xhr/send-content-type-charset.htm.ini
@@ -2,17 +2,11 @@
   [charset given but wrong, fix it (unknown MIME, bogus charset)]
     expected: FAIL
 
-  [charset given but wrong, fix it (known MIME, actual charset)]
-    expected: FAIL
-
   [Multiple non-UTF-8 charset parameters deduplicate, bogus parameter dropped]
     expected: FAIL
 
   [charset with leading space that is UTF-8 does change]
     expected: FAIL
 
-  [charset in double quotes with space]
-    expected: FAIL
-
   [unknown parameters need to be preserved]
     expected: FAIL
diff --git a/tests/wpt/meta/xhr/setrequestheader-content-type.htm.ini b/tests/wpt/meta/xhr/setrequestheader-content-type.htm.ini
deleted file mode 100644
index 35bb7bb2a51..00000000000
--- a/tests/wpt/meta/xhr/setrequestheader-content-type.htm.ini
+++ /dev/null
@@ -1,12 +0,0 @@
-[setrequestheader-content-type.htm]
-  [String request keeps setRequestHeader() Content-Type, with charset adjusted to UTF-8]
-    expected: FAIL
-
-  [XML Document request keeps setRequestHeader() Content-Type, with charset adjusted to UTF-8]
-    expected: FAIL
-
-  [HTML Document request keeps setRequestHeader() Content-Type, with charset adjusted to UTF-8]
-    expected: FAIL
-
-  [URLSearchParams request keeps setRequestHeader() Content-Type, with charset adjusted to UTF-8]
-    expected: FAIL
diff --git a/tests/wpt/tests/xhr/setrequestheader-content-type.htm b/tests/wpt/tests/xhr/setrequestheader-content-type.htm
index 07238391eb5..c7848214246 100644
--- a/tests/wpt/tests/xhr/setrequestheader-content-type.htm
+++ b/tests/wpt/tests/xhr/setrequestheader-content-type.htm
@@ -206,15 +206,6 @@
         "application/x-www-form-urlencoded;charset=UTF-8",
         'URLSearchParams request has correct default Content-Type of "application/x-www-form-urlencoded;charset=UTF-8"'
       )
-      request(
-        function _URLSearchParams() { return new URLSearchParams("q=testQ&topic=testTopic") },
-        {"Content-Type": "application/xml;charset=ASCII"},
-        "application/xml;charset=UTF-8",
-        "URLSearchParams request keeps setRequestHeader() Content-Type, with charset adjusted to UTF-8"
-        // the default Content-Type for URLSearchParams has a charset specified (utf-8) in
-        // https://fetch.spec.whatwg.org/#bodyinit, so the user's must be changed to match it
-        // as per https://xhr.spec.whatwg.org/#the-send%28%29-method step 4.
-      )
     </script>
   </body>
 </html>