How can I wrap only the X axis using Classic2d noise?

I'm using AdvancedRandom.Classic2d(x,y) (with x and y being my tile coordinates) to generate reasonably good maps, but I want the map to be horizontally tileable (not vertical).

It seems simple to gradually interpolate the left and right edges but I can't find a good solution within C3.

Here is what I mean, this is the same map tiled next to itself: