diff --git a/Tests/LibWeb/Text/expected/fetch-response-content-type.txt b/Tests/LibWeb/Text/expected/fetch-response-content-type.txt
new file mode 100644
index 00000000000..26b1f59734c
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/fetch-response-content-type.txt
@@ -0,0 +1,2 @@
+text/html
+text/plain
diff --git a/Tests/LibWeb/Text/input/fetch-response-content-type.html b/Tests/LibWeb/Text/input/fetch-response-content-type.html
new file mode 100644
index 00000000000..a809b5555a8
--- /dev/null
+++ b/Tests/LibWeb/Text/input/fetch-response-content-type.html
@@ -0,0 +1,18 @@
+<script src="include.js"></script>
+<script>
+    test(() => {
+        const data = ["<h1>Well hello friends!</h1>"];
+        const blob = new Blob(data, { type: "text/html" });
+
+        const response1 = new Response(blob);
+
+        const response2 = new Response(blob, {
+            headers: {
+                "Content-Type": "text/plain",
+            },
+        });
+
+        println(response1.headers.get("Content-Type"));
+        println(response2.headers.get("Content-Type"));
+    });
+</script>
diff --git a/Userland/Libraries/LibWeb/Fetch/Response.cpp b/Userland/Libraries/LibWeb/Fetch/Response.cpp
index 839ee6f3133..4acc5c24b87 100644
--- a/Userland/Libraries/LibWeb/Fetch/Response.cpp
+++ b/Userland/Libraries/LibWeb/Fetch/Response.cpp
@@ -113,7 +113,7 @@ WebIDL::ExceptionOr<void> Response::initialize_response(ResponseInit const& init
         m_response->set_body(body->body);
 
         // 3. If body’s type is non-null and response’s header list does not contain `Content-Type`, then append (`Content-Type`, body’s type) to response’s header list.
-        if (body->type.has_value() && m_response->header_list()->contains("Content-Type"sv.bytes())) {
+        if (body->type.has_value() && !m_response->header_list()->contains("Content-Type"sv.bytes())) {
             auto header = Infrastructure::Header {
                 .name = MUST(ByteBuffer::copy("Content-Type"sv.bytes())),
                 .value = MUST(ByteBuffer::copy(body->type->span())),