A cell cycle checkpoint that detects septin defects and responds by inhibiting the mitotic cyclin-dependent kinase (CDK). In Saccharomyces cerevisiae, correct formation of a functional septin cytoskeleton permits the cell to switch to isotropic bud growth and the onset of mitotic chromosome segregation. In the presence of septin defects, the mitotic CDK is inhibited and both the switch to isotropic bud growth and the onset of mitotic chromosome segregation is delayed.