I would like to open source my software library under the LGPL license. But I'm not sure if I'm allowed to use that license, as my library uses another library which is currently closed sourced. By using I mean that my library has a dependency on that closed sourced, third-party library. I won't be able to distribute the third-party library, but I hope that they will open source it some time later.

What am I allowed to do in this case?

  • 2
    This may be perfectly fine, or may require you to add an exception to the LGPL. If you need to add an exception, you will not be able to use other LGPL-licensed code in your library. Could you explain a bit more how the proprietary library is used, and how users might obtain it?
    – amon
    Jun 25, 2019 at 10:03
  • 1
    What do you mean by "use"? Are you going to distribute the closed source library too? As an example, many (most) LGPL libraries designed to be used on Windows use closed source libraries from Microsoft, but they don't distribute these.
    – Brandin
    Jun 26, 2019 at 7:08
  • Thanks for your comments. I've added some more information on my post. Do these answer your questions?
    – JoLau
    Jun 26, 2019 at 11:10
  • 1. Which version of the LGPL do you want to use (v2, v3). 2. Do you think the library you want to link to could be considered a "system library"? See gnu.org/licenses/gpl-faq.html#SystemLibraryException
    – Brandin
    Jun 26, 2019 at 11:26
  • Another possibility is if you consider this closed source library a plug-in or not. The GPL FAQ describes your situation as a "borderline case", assuming you try to consider the library and your library to be separate programs not creating a combined work: gnu.org/licenses/gpl-faq.html#GPLPlugins
    – Brandin
    Jun 26, 2019 at 11:30

1 Answer 1


Presumably the license under which you got the closed source forbids such use.

Depending on the exact relationship of your code and said library, it might fall under "mere use" of it (in which case it would be OK) or some more intimate relation (in which case you would have to distribute the closed part as LGPL too).

Note that I don't know full details, I'm not your lawyer, so take this as a guess and encouragement to look further into the matter.

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