The Free Software Foundation says it is on track to build Apache License compatibility into the upcoming GPL version 3, despite "11th-hour" problems that scuppered the feature in the latest GPL 3 draft.

The GPL is the most widely used open source licence, and the Apache License, besides covering the immensely popular Apache web server, is also a well-established licence. The incompatibility between the two has long caused headaches for developers, since it means code can't be shared between projects covered by one licence or the other.

Apache License compatibility was one of the major features planned for the latest draft of the GPL 3, released in March, and its absence came as a surprise.

But the FSF said on Tuesday that compatibility will make it into the final version of the GPL 3.

"I think a final change we'll see before the GPL 3 release will be that compatibility," said FSF executive director Peter Brown during a panel discussion at the JavaOne conference in San Francisco on Tuesday.

Compatibility had been removed from the latest GPL 3 draft because of a last-minute legal problem, according to the FSF. Another problem has been that the issue has simply fallen through the cracks in the mammoth GPL 3 drafting process, according to the FSF and the Apache Foundation.

Cliff Schmidt, vice president of legal affairs for the Apache Software Foundation, said during the panel discussion that the two organisations are now working together to make compatibility happen.

In practice, compatibility is likely to be a one-way street, with the more tightly restricted GPL projects able to take code from Apache License projects, but not the other way around.

In March the FSF released the next-to-last rough draft of the GPL 3, including alterations specifically designed to put a stop to future patent deals of the sort that Novell and Microsoft agreed to last year.

The latest draft also softened up some other intellectual property provisions, to the point where some who had previously opposed the licence - such as Linus Torvalds - were now taking a more positive view.

The final version of the licence is currently set to be finalised in August.