diff --git a/utils/treesitter/src/scanner.c b/utils/treesitter/src/scanner.c
index 36d885029f80..65fd3a26bb52 100644
--- a/utils/treesitter/src/scanner.c
+++ b/utils/treesitter/src/scanner.c
@@ -11,7 +11,7 @@ enum TokenType {
 };
 
 // our scanner is stateless
-void* tree_sitter_carbon_external_scanner_create() { return NULL; }
+void* tree_sitter_carbon_external_scanner_create(void) { return NULL; }
 
 unsigned tree_sitter_carbon_external_scanner_serialize(
     __attribute__((unused)) void* payload,