A roof anchor with a channel fits over a roof panel rib typically having a rib head supported by a narrower rib neck. Setscrews on the anchor side thread through matching threaded holes in anchor sides and into the channel, sandwiching a roof panel rib therebetween when it is received into the channel. To prevent the anchor from lifting off the roof panel rib, the setscrews are located on the anchor sides low in the anchor channel engaging the roof panel rib at the narrow rib neck such that the roof panel rib head can be received between the setscrews and the anchor top. A rib bar typically shaped to functionally match the roof panel rib may be inserted within the roof panel rib as a brace to prevent a roof panel rib from collapsing under force of the setscrews.