diff --git a/admin_manual/configuration_files/external_storage_configuration.rst b/admin_manual/configuration_files/external_storage_configuration.rst
index da4525cb8..6aa829c7a 100644
--- a/admin_manual/configuration_files/external_storage_configuration.rst
+++ b/admin_manual/configuration_files/external_storage_configuration.rst
@@ -182,6 +182,10 @@ Example
 .. note:: A non-blocking or correctly configured SELinux setup is needed
    for this backend to work.
 
+.. note:: The external storage ``FTP/FTPS/SFTP`` needs the ``allow_url_fopen`` PHP
+   setting to be set to ``1``. When having connection problems make sure that it is
+   not set to ``0`` in your ``php.ini``.
+
 SFTP
 ~~~~
 
@@ -214,6 +218,10 @@ Example
 
 .. note:: PHP needs to be build with SFTP support for this backend to work.
 
+.. note:: The external storage ``FTP/FTPS/SFTP`` needs the ``allow_url_fopen`` PHP
+   setting to be set to ``1``. When having connection problems make sure that it is
+   not set to ``0`` in your ``php.ini``.
+
 SMB
 ~~~
 The SMB backend mounts a folder on a remote Samba server, a NAS appliance or
diff --git a/admin_manual/configuration_files/external_storage_configuration_gui.rst b/admin_manual/configuration_files/external_storage_configuration_gui.rst
index 3dfe80743..a1c940d49 100644
--- a/admin_manual/configuration_files/external_storage_configuration_gui.rst
+++ b/admin_manual/configuration_files/external_storage_configuration_gui.rst
@@ -198,6 +198,10 @@ Connecting to an FTP server requires:
 .. note:: A non-blocking or correctly configured SELinux setup is needed
    for this backend to work.
 
+.. note:: The external storage ``FTP/FTPS/SFTP`` needs the ``allow_url_fopen`` PHP
+   setting to be set to ``1``. When having connection problems make sure that it is
+   not set to ``0`` in your ``php.ini``.
+
 .. figure:: ../images/external-storage-ftp.png
 
 SFTP uses SSH rather than SSL, as FTPS does, so your SFTP sessions are always