Black frames when exporting at 60 FPS

My video file that I imported into Premiere Pro is at 59.71 FPS. When I export, it tries to export at 59.94 FPS, and I end up with black frames sporadically appearing throughout the video. How do I set up Premiere Pro to automatically use my original FPS? I thought that it would do it automatically, but it was originally at 29.97 FPS, which isn't what I need.