Changes have been made to this year’s Higher English exam paper over concerns that some questions were leaked.
The Scottish Qualifications Authority (SQA) said action was taken to “ensure the integrity of qualifications”.
Thousands of pupils will sit the exam at schools and colleges across the country on Thursday.
Candidates are being told not to be anxious about the changes.
There are two papers in the English Higher which are sent out to schools before the date of the exam.
It was reported that the SQA had concerns that some of the questions could have been leaked, and it created a new version of one of the papers last month.
An SQA spokesman said: “A potential issue with one of the Higher English question papers was identified.
“We made the appropriate adjustments and a new paper was distributed to centres. Our chief invigilators have been informed.
“We have robust procedures in place to ensure the integrity of our qualifications. We took swift and appropriate action, meaning candidates will sit the examination as intended.”
Last year, the exams agency faced criticism for setting a maths paper which was far harder than pupils and teachers had expected.
When the results were sent out in August, it was revealed that the pass mark for the new Higher maths qualification had been lowered to just 34% due to its difficulty.
Teaching union the EIS said the most important issue is to ensure the paper is fair to all candidates.
General secretary Larry Flanagan said: “Where there is doubt over an element of an examination paper, the sensible option is to replace that section of the paper.
“The most important consideration is that no pupil is unfairly advantaged or disadvantaged, so that the exam can deliver a fair measure of each pupil’s level of attainment.
“Clearly, there will have to be a thorough investigation into the circumstances that led to this situation, but the most important issue in the short term is to ensure that any issues with the paper are rectified.”