diff --git a/lib/remote/httpconnection.cpp b/lib/remote/httpconnection.cpp
index 654988ca4b9..6aee8a19c03 100644
--- a/lib/remote/httpconnection.cpp
+++ b/lib/remote/httpconnection.cpp
@@ -149,6 +149,7 @@ void HttpConnection::ProcessMessageAsync(HttpRequest& request)
 
 	if (!user) {
 		response.SetStatus(401, "Unauthorized");
+		response.AddHeader("Content-Type", "text/html");
 		response.AddHeader("WWW-Authenticate", "Basic realm=\"Icinga 2\"");
 		String msg = "<h1>Unauthorized</h1>";
 		response.WriteBody(msg.CStr(), msg.GetLength());
diff --git a/lib/remote/httphandler.cpp b/lib/remote/httphandler.cpp
index fde43c2b503..d785952acc5 100644
--- a/lib/remote/httphandler.cpp
+++ b/lib/remote/httphandler.cpp
@@ -88,6 +88,7 @@ void HttpHandler::ProcessRequest(const ApiUser::Ptr& user, HttpRequest& request,
 
 	if (!handler || (!exact_match && !handler->CanAlsoHandleUrl(request.RequestUrl))) {
 		response.SetStatus(404, "Not found");
+		response.AddHeader("Content-Type", "text/html");
 		String msg = "<h1>Not found</h1>";
 		response.WriteBody(msg.CStr(), msg.GetLength());
 		response.Finish();