The structure of the cell wall has a major impact on plant growth and development, and alteration of cell wall structural components is often detrimental to biomass production. However, the molecular mechanisms responsible for these negative effects are largely unknown. Arabidopsis thaliana plants with altered pectin composition, due to either the expression of a fungal polygalacturonase (35S:AnPGII plants) or a mutation in the QUASIMODO2 gene that encodes a putative pectin methyl-transferase (qua2-1 plants), display severe growth defects. Here we show that expression of AtPRX71, encoding a class III peroxidase, strongly increases in 35S:AnPGII and qua2-1 plants, as well as in response to treatments with the cellulose synthase inhibitor isoxaben, which also impairs cell wall integrity. Analysis of atprx71 loss-of-function mutants and of plants overexpressing AtPRX71 indicates that this gene negatively influences Arabidopsis growth at different stages of development, likely limiting cell expansion. The atprx71-1 mutation partially suppresses the dwarf phenotype of qua2-1, suggesting that AtPRX71 contributes to the growth defects observed in plants undergoing cell wall damage. Furthermore, AtPRX71 appears to promote the production of reactive oxygen species in qua2-1 plants as well as in plants treated with isoxaben. We propose that AtPRX71 contributes to strengthen cell walls, therefore restricting cell expansion, during both normal growth and in response to cell wall damage.