I have dual-licensed library, LGPL 3 and commercial license. Someone downloads the LGPL version, makes some improvements and sends back few patches. So far so good. But what now? It's legal to just merge those patches into code base and use them under commercial license?

I know some project (Qt, Canonical) have contributor agreements to handle exactly this cases. But what's the situation if this library doesn't have contributor agreements?



1 Answer 1


IANAL, but as far as I understand you should ask the contributer to assign the copyrights of the changes to you, refusing to merge if they doesn't. Once the copyrights are you, you can distribute in whatever license you want.

  • 1
    so if I understand correctly, if he refuses to do so, I can use his patch only for LGPL version and must keep it out of the proprietary? so basically maintain two code bases from that point? seems fair enough, thank you
    – graywolf
    Jun 30, 2015 at 10:29
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    From a business point-of-view, if you do start incorporating the patches into the LGPL version only, then before long the LGPL version will have more features and fewer bugs than the commercial one. Customers may then start asking why they are paying extra for the commercial one.
    – Simon B
    Jun 30, 2015 at 10:34
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    If he refuses to do so, you don't merge. Maintaining two parallel code bases is a pain, since every new commit will have to be tested against both, and even if other LGPL contributers agree to assign the copyrights to you they didn't buy the proprietary version so they can't test against it - and they also don't have the incentive to do so. ...
    – Idan Arye
    Jun 30, 2015 at 11:09
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    ... So, if the contributor won't assign the copyrights to you - just don't merge! You don't want to lose the legal control over your project just to merge some patch. The contributor shouldn't mind - they'll be able to use their patch via the LGPL version, and if they fear you'll ever remove that version - well, in that case the patch will be useful to them even if they do retain copyrights over it.
    – Idan Arye
    Jun 30, 2015 at 11:10

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