The inflammasomes are signaling platforms that promote the activation of inflammatory caspases such as caspases-1, -4, -5, and -11, which cleave gasdermin D (GSDMD) to induce pyroptotic cell death. The mechanisms of GSDMD recognition by inflammatory caspases remain poorly understood. Here, we demonstrate that the catalytic domains of inflammatory caspases can directly bind to GSDMD or its cleavage site peptide, FLTD. A GSDMD-derived inhibitor, N -acetyl-Phe-Leu-Thr-Asp-chloromethylketone (Ac-FLTD-CMK), inhibits GSDMD cleavage in vitro and suppresses pyroptosis downstream of both canonical and noncanonical inflammasomes. By contrast, the inhibitor does not target caspase-3 or apoptosis, suggesting that it is specific for inflammatory caspases. Structure of caspase-1 in complex with Ac-FLTD-CMK reveals extensive enzyme–inhibitor interactions that shed light on GSDMD recognition by inflammatory caspases.