Are marine heatwaves really becoming more common? A 2018 study reported that the ocean now has many more “marine-heatwave days” — days when the sea surface is unusually hot — than it used to. We re-checked that finding using completely different data and a different program, and it holds up. What was tested — One specific finding from the 2018 paper: that between 1982 and 2016 the world's oceans gained roughly 30 more marine-heatwave days a year. We did not test the paper's better-known headline — a 54% rise measured back over a whole century — because that one cannot be checked independently; we explain why in “What we did not test”. What was found — It is confirmed. Using satellite sea-surface temperatures from the European Space Agency's climate record (not the American data the original used) and a separate, independent piece of software to spot the heatwaves, we measured almost the same rise — about 32 extra marine-heatwave days over the period, against the 30 the original reported, a difference of about 6%. The frequency and the length of heatwaves also went up, matching the original. Does natural variability explain it? — No. When we removed the effect of El Niño and La Niña — the natural warm/cool swings in the Pacific — the rise was only slightly smaller and was still there. So the trend is not just a side-effect of those cycles. Why this carries weight — The two studies share neither the data nor the software, so their agreement is evidence about the finding itself, not a mistake copied from one to the other. A shared dataset or shared code could hide the same error in both; here nothing was shared. What we did not test — The paper's famous “54% over the past century” figure needs daily temperature records from before 1981, and no independent global record that far back exists — for anyone. So we tested only the satellite era (about a third of the paper's span) and say so plainly, rather than claiming more than the data allows. Different data, different software, same answer: marine-heatwave days really are rising.