A manual safety system for reducing the chances of inadvertent discharge of a linear striker fired semi-automatic or automatic pistol equipped with the system. An otherwise conventional pistol is modified by structural changes in the trigger mechanism housing and by the addition of a trigger bar guide, a manually movable safety lever, a pressure plate and a spring. The trigger bar guide and safety lever are mounted to the trigger mechanism housing for linear and pivotal movement, respectively. A portion of the conventional trigger bar, which must be moved in order to effect firing movement of the trigger, is engaged with and blocked by the trigger bar guide which in turn is engaged and blocked by a portion of the safety lever. In order to unblock and enable the firing system, the safety lever is moved by applying pressure to a tab serving as a thumb rest. Rotation of the safety lever disengages it from the trigger bar guide, permitting rearward movement of the guide and the trigger bar and firing movement of the trigger.