diff --git a/crates/sylpheed-formats/Cargo.toml b/crates/sylpheed-formats/Cargo.toml
index 1cd5d220..b08124e6 100644
--- a/crates/sylpheed-formats/Cargo.toml
+++ b/crates/sylpheed-formats/Cargo.toml
@@ -11,7 +11,12 @@ xdvdfs    = { workspace = true }
 binrw     = { workspace = true }
 flate2    = "1"                     # zlib/DEFLATE for IPFB "Z1" entries (miniz_oxide backend, WASM-safe)
 ttf-parser = { version = "0.24", default-features = false, features = ["std", "opentype-layout"] } # font metadata (OTF/TTF/ttcf), WASM-safe
-tokio     = { workspace = true }
+# tokio is a DEV dependency only (see [dev-dependencies] below). Every use in
+# this crate is inside a `mod tests`: three runtime builders in ship.rs and one
+# `#[tokio::test]` in xiso.rs. As a normal dependency it pulled `tokio/full`,
+# whose `net` feature drags in `mio`, which does not build for wasm32 —
+#   error: This wasm target is unsupported by mio.
+# so the unused dependency was breaking the WASM job.
 futures   = { workspace = true }
 thiserror = { workspace = true }
 anyhow    = { workspace = true }