A modular rotary cutter bed is formed by a series of essentially identical cutter modules mounted end-to-end along the length of a common support beam. Guards for the cutters of the modules are arranged such that each guard overlaps and bridges the seam between an adjacent pair of modules so as to increase the structural rigidity of the cutter bed. Each guard is attached at its front end to the noses of a pair of adjacent modules and at its rear end to the support beam to increase structural integrity in all directions. A second embodiment does not utilize a common support beam for the modules but instead relies upon the interconnections between adjacent modules and bridging overlap of the guards to rigidify the cutter bed.