diff --git a/lib/who_need_help_web/security_headers.ex b/lib/who_need_help_web/security_headers.ex
index 963ee70..41b997f 100644
--- a/lib/who_need_help_web/security_headers.ex
+++ b/lib/who_need_help_web/security_headers.ex
@@ -9,15 +9,14 @@ defmodule WhoNeedHelpWeb.SecurityHeaders do
       |> Application.fetch_env!(:map_tile_url)
       |> origin()
 
-    websocket_origins =
-      [
-        origin(%URI{scheme: "ws", host: conn.host, port: conn.port}),
-        origin(%URI{scheme: "wss", host: conn.host, port: default_https_port(conn)})
-      ]
-      |> Enum.reject(&is_nil/1)
-      |> Enum.uniq()
+    websocket_origin =
+      case conn.scheme do
+        :http -> origin(%URI{scheme: "ws", host: conn.host, port: conn.port})
+        :https -> origin(%URI{scheme: "wss", host: conn.host, port: conn.port})
+        _other -> nil
+      end
 
-    connect_sources = sources(["'self'", tile_origin | websocket_origins])
+    connect_sources = sources(["'self'", tile_origin, websocket_origin])
     image_sources = sources(["'self'", "data:", "blob:", tile_origin])
 
     policy =
@@ -39,9 +38,6 @@ defmodule WhoNeedHelpWeb.SecurityHeaders do
     put_resp_header(conn, "content-security-policy", policy)
   end
 
-  defp default_https_port(%Plug.Conn{port: 443}), do: 443
-  defp default_https_port(_conn), do: nil
-
   defp sources(values),
     do: values |> Enum.reject(&is_nil/1) |> Enum.uniq() |> Enum.join(" ")
 
diff --git a/test/who_need_help_web/controllers/page_controller_test.exs b/test/who_need_help_web/controllers/page_controller_test.exs
index 4a2cbb2..d74232e 100644
--- a/test/who_need_help_web/controllers/page_controller_test.exs
+++ b/test/who_need_help_web/controllers/page_controller_test.exs
@@ -13,6 +13,8 @@ defmodule WhoNeedHelpWeb.PageControllerTest do
     refute content_security_policy =~ "script-src 'self' 'unsafe-inline'"
     assert content_security_policy =~ "frame-ancestors 'none'"
     assert content_security_policy =~ "https://tile.openstreetmap.org"
+    assert content_security_policy =~ "ws://www.example.com"
+    refute content_security_policy =~ "wss://www.example.com"
 
     assert get_resp_header(conn, "permissions-policy") == [
              "geolocation=(self), camera=(), microphone=(), payment=(), usb=()"
@@ -38,6 +40,20 @@ defmodule WhoNeedHelpWeb.PageControllerTest do
            ) == 1
   end
 
+  test "HTTPS content security policy permits only secure WebSockets", %{conn: conn} do
+    conn =
+      conn
+      |> Map.put(:scheme, :https)
+      |> Map.put(:host, "help.example")
+      |> Map.put(:port, 443)
+      |> WhoNeedHelpWeb.SecurityHeaders.put_content_security_policy([])
+
+    [content_security_policy] = get_resp_header(conn, "content-security-policy")
+
+    assert content_security_policy =~ "wss://help.example"
+    refute content_security_policy =~ "ws://help.example"
+  end
+
   test "Phoenix logs filter authentication and handover secrets" do
     assert Phoenix.Logger.filter_values(%{
              "password" => "not-logged",