Django ugettext_lazy with concatenated strings

I have searched for an answer before posting this question. There is a bunch of long strings that are split in the following way and need to be translated

string = "This is a very long " \
          "string to be translated"

after marking

string = _("This is a very long " \
          "string to be translated")

the resulting .po file keeps only the first part of the string

msgid "This is a very long "
msgstr ""

So, is there any way to make this work, preferably without messing up the code very much...

Thank you