When plant cell walls are damaged by mechanical or biochemical means, the cells initiate adaptive responses to repair the walls and prevent infection. Whereas the cell wall integrity (CWI) maintenance mechanism monitors the status of the cell wall and initiates adaptive cellular responses to damage, pattern-triggered immunity (PTI) induces both cellular and systemic responses that limit infection. Engelsdorf et al. found that osmosensitive alterations in the mechanical properties of the cell wall were important for inducing the adaptive responses to cell wall damage. The receptor-like kinases THE1 and FEI2 and the ion channel MCA1 were required for stimulating CWI-dependent responses to damage. Cell wall damage also induced the expression of host defense peptides that promoted PTI and dampened CWI-dependent processes. The CWI mechanism still elicited damage responses even when PTI was impaired, suggesting that it serves as a failsafe to protect plants even if the immune response is compromised.