Severe cases of coronavirus disease 2019 (COVID-19) are characterized by a hyperinflammatory immune response that leads to numerous complications. Production of proinflammatory neutrophil extracellular traps (NETs) has been suggested to be a key factor in inducing a hyperinflammatory signaling cascade, allegedly causing both pulmonary tissue damage and peripheral inflammation. If true, finding ways to inhibit NET production could provide therapeutic strategies to prevent respiratory damage and death from SARS-CoV-2 related inflammation. Here, we demonstrate that synthetic glycopolymers that activate signaling of the neutrophil checkpoint receptor Siglec-9 suppress NETosis induced by agonists of viral TLR receptors and COVID-19 plasma. Thus, Siglec-9 represents an attractive therapeutic target to curb neutrophilic hyperinflammation in COVID-19.