Global warming increases the risk of wildfire and insect outbreaks, potentially reducing the carbon storage function of coarse woody debris (CWD). There is an increasing focus on the interactive effects of wildfire and insect infestation on forest carbon, but the impact of wood-boring beetle tunnels via their effect on the flammability of deadwood remains unexplored. We hypothesized that the presence of beetle holes, at natural densities, can affect its flammability positively through increased surface area and enhanced oxygen availability in the wood. To test this, wood-boring beetle holes were mimicked experimentally in decaying logs of two coniferous species, and flammability variables of these treated logs were compared. We found that wood-boring beetles partly increased the flammability of CWD of both species (via promoting deadwood smoldering combustion) when their holes were parallel with the airflow. Even when accounting for the influences of wood density and cracks, these radial holes continued to have a notable impact on deadwood flammability. While these holes did not make the wildfire more intense, they significantly increased carbon loss during combustion. This suggests that wood-boring beetles will enhance carbon release from deadwood into the atmosphere during wildfire., (© 2025 The Author(s). Ecology published by Wiley Periodicals LLC on behalf of The Ecological Society of America.)