diff --git a/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.cpp b/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.cpp
index d7224f87a5..309be13573 100644
--- a/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.cpp
+++ b/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.cpp
@@ -291,4 +291,21 @@ String XMLHttpRequest::get_all_response_headers() const
     return builder.to_string();
 }
 
+// https://xhr.spec.whatwg.org/#dom-xmlhttprequest-overridemimetype
+DOM::ExceptionOr<void> XMLHttpRequest::override_mime_type(String const& mime)
+{
+    // 1. If this’s state is loading or done, then throw an "InvalidStateError" DOMException.
+    if (m_ready_state == ReadyState::Loading || m_ready_state == ReadyState::Done)
+        return DOM::InvalidStateError::create("Cannot override MIME type when state is Loading or Done.");
+
+    // 2. Set this’s override MIME type to the result of parsing mime.
+    m_override_mime_type = MimeSniff::MimeType::from_string(mime);
+
+    // 3. If this’s override MIME type is failure, then set this’s override MIME type to application/octet-stream.
+    if (!m_override_mime_type.has_value())
+        m_override_mime_type = MimeSniff::MimeType("application"sv, "octet-stream"sv);
+
+    return {};
+}
+
 }
diff --git a/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.h b/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.h
index 62e7e420b4..5c980701bd 100644
--- a/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.h
+++ b/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.h
@@ -14,6 +14,7 @@
 #include <LibWeb/Bindings/Wrappable.h>
 #include <LibWeb/DOM/EventTarget.h>
 #include <LibWeb/DOM/ExceptionOr.h>
+#include <LibWeb/MimeSniff/MimeType.h>
 #include <LibWeb/XHR/XMLHttpRequestEventTarget.h>
 
 namespace Web::XHR {
@@ -62,6 +63,8 @@ public:
     Bindings::CallbackType* onreadystatechange();
     void set_onreadystatechange(Optional<Bindings::CallbackType>);
 
+    DOM::ExceptionOr<void> override_mime_type(String const& mime);
+
 private:
     virtual void ref_event_target() override { ref(); }
     virtual void unref_event_target() override { unref(); }
@@ -91,6 +94,9 @@ private:
     bool m_timed_out { false };
 
     ByteBuffer m_response_object;
+
+    // https://xhr.spec.whatwg.org/#override-mime-type
+    Optional<MimeSniff::MimeType> m_override_mime_type;
 };
 
 }
diff --git a/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.idl b/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.idl
index 9e1e0ec14c..df794fd04d 100644
--- a/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.idl
+++ b/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.idl
@@ -18,6 +18,7 @@ interface XMLHttpRequest : XMLHttpRequestEventTarget {
 
     ByteString? getResponseHeader(ByteString name);
     ByteString getAllResponseHeaders();
+    undefined overrideMimeType(DOMString mime);
 
     attribute EventHandler onreadystatechange;