With this trick your pattern making gets easier and you'll never have to worry about unwonted borderlines. It works for Inkscape and Illustrator as well.

Some of you might be familiar with this issue already; sometimes, while making a pattern in Illustrator or similar programs, a 1 pixel line hides in the border of your repeating pattern. Sometimes it's light, sometimes it's dark and one asks one's self where this thing came from. The tiniest inaccuracies in creating the image, as well as the method that the software uses to create a pixel image from vector data are usually to blame. Transparencies can also play a role. But never fear; these little frustrations can be managed, and in the process you might save yourself a bit of extra work :)