London Stock Exchange Group and Deutsche Boerse have agreed to lower the level of approvals they need from the German exchange's investors to push through their planned merger.
The companies have reduced the approval threshold to 60% from an earlier minimum of 75%.
They are trying to keep the merger on track following Britain's vote to leave the European Union and concerns from Germany's markets regulator.
"This change in procedure is a purely technical one. We are confident that we will reach the 75% threshold in the course of the full tender process," Deutsche Boerse CFO Gregor Pottmeyer said today.
Financial regulators in Germany and Britain, along with European Union competition authorities, are likely to pose a sterner challenge to the $27 billion merger.
German markets regulator BaFin last month said it was hard to see how the head office of the merged group could be in London given that Britain was leaving the EU.
Deutsche Boerse said yesterday it was concerned that the 75% threshold might prove difficult to secure because index funds which hold up to 15% of its shares are unable to accept the offer until the minimum level of acceptances has been reached.
Shareholders in the British company approved the plan at a subdued, short meeting last week despite uncertainties after the EU referendum result.
Deutsche Boerse had asked its shareholders to back the deal - the third attempt by the LSE to merge with the German exchange operator in some 16 years - in a postal vote that had been due to close on July 12.
However, the acceptance period is being extended for a further two weeks to July 26.
Terms of the deal cannot be changed until the merger closes around the end of June next year.
Deutsche Boerse and LSE officials have signalled they are willing to do whatever it takes to get the green light from regulators.
The two companies are looking at how they could reassure regulators that a merged company would actually implement any structural changes such as the location of the head office agreed before the deal closes.
A source familiar with the process said one idea would be for a legal undertaking to regulators, similar to a "living will" banks must now write for regulators, setting out what would happen if it got into trouble.
