If you have the sear block with the 1/8" plunger it should allow a safety to be added. You can go to speedshootersupply.com and order the parts, about $25 plus shipping. It's something I also want to do since my 4 other M&P's have safeties. If you look on how the sear block fits into the frame you should be able to see some space on each side under the slide rails and that is where the safety fits.