diff --git a/scripts/ci-test.sh b/scripts/ci-test.sh
index 52e3548..3c557d8 100755
--- a/scripts/ci-test.sh
+++ b/scripts/ci-test.sh
@@ -89,6 +89,7 @@ run_step "cargo clippy (fast-deflate / zlib-ng)" cargo clippy \
 # that: fail if a crate that compiles C (a *-sys crate, cc or cmake) enters the
 # default dependency tree of any of them. clawhdf5-migrate (bundled SQLite),
 # clawhdf5-napi (Node) and clawhdf5-gpu (graphics drivers) are exempt.
+# js-sys (clawhdf5-wasm's bindings to JavaScript) builds no C.
 no_c_in_default_build() {
     local crate found=0
     for crate in clawhdf5-format clawhdf5-io clawhdf5-filters clawhdf5 \
@@ -96,7 +97,8 @@ no_c_in_default_build() {
         clawhdf5-wasm; do
         local c_deps
         c_deps=$(cargo tree -q -p "$crate" -e normal,build --prefix none \
-            | grep -E '^([a-z0-9_-]+-sys|cc|cmake) v' | sort -u)
+            | grep -E '^([a-z0-9_-]+-sys|cc|cmake) v' \
+            | grep -v '^js-sys v' | sort -u)
         if [ -n "$c_deps" ]; then
             echo "$crate pulls in C by default:"
             echo "$c_deps" | sed 's/^/    /'