The yeast mitochondrial outer membrane (MOM) protein Mdm10 has been shown to have important roles in different aspects of mitochondrial function, including mitochondrial biogenesis and mitochondrial lipid homeostasis – a role it exerts as a component of the so-called ER-mitochondria encounter structure (ERMES). Consequently, mdm10Δ mutants show severe growth defects. However, because the functions of Mdm10 are related and interlinked, its primary role in mitochondria remains unclear. In this study (p. 3563), Doron Rapaport, Kai Stefan Dimmer and co-workers perform a systematic screen for suppressors of the growth phenotype in mdm10Δ cells. They find two new proteins with, thus far, unknown functions, which they call Mdm10 complementing proteins 1 and 2 (Mcp1 and Mcp2, respectively). Both Mcp1 and Mcp2 localise to mitochondrial membranes. Mcp1 is a MOM protein, with its C-terminus facing the intermembrane space, whereas Mcp2 is an integral protein of the mitochondrial inner membrane. They find that overexpression of Mcp1 and Mcp2 rescued mitochondrial morphology, and restored mitochondrial phospholipid and ergosterol homeostasis in mdm10Δ cells. The authors also show that there are genetic interactions between MCP1 or MCP2 and other ERMES components, and their findings suggest that the ERMES complex is also involved in mitochondrial ergosterol homeostasis. Taken together, these data provide new insights into the mechanism of lipid homeostasis in mitochondria.