Europe’s satellite navigation system, ‘Galileo,’ has been finally restored six days after a major technical error caused most satellites powering the system to break down.

The European Global Navigation Satellite Systems Agency (GNSS) announced that initial services had been restored on Thursday morning, but added that users may still “experience service instability until further notice.”

The EU’s Galileo system was built to replace the US’ GPS navigation in a multi-billion-euro project that went live in December 2016 after 17 years of development. However, users were automatically reverted to the US positioning system during the almost week-long outage.

The GNSS announced the outage on Sunday, explaining that “a technical incident related to its ground infrastructure” had caused a “temporary interruption” of services since Friday, July 12.

There are currently 22 operational satellites in orbit, with another two in testing and a further 12 under construction. Owned by the EU and operated by the European Space Agency, the full service is expected to be deployed by 2020.