diff --git a/.gitea/workflows/ci.yml b/.gitea/workflows/ci.yml
index 1a7cdde..fcc2d23 100644
--- a/.gitea/workflows/ci.yml
+++ b/.gitea/workflows/ci.yml
@@ -31,7 +31,9 @@ jobs:
           # cmake builds libz-ng-sys for the opt-in `fast-deflate` (zlib-ng)
           # steps in ci-test.sh; rust:latest does not ship it. The default
           # build (pure-Rust zlib-rs) does not need it.
-          apt-get install -y --no-install-recommends python3 python3-venv cmake
+          # hdf5-tools: h5ls/h5stat/h5dump/h5diff, which the h5rs
+          # (clawhdf5-tools) interop tests compare against.
+          apt-get install -y --no-install-recommends python3 python3-venv cmake hdf5-tools
           python3 -m venv /opt/interop
           /opt/interop/bin/pip install --no-cache-dir h5py numpy netCDF4 xarray hdf5plugin
           echo "/opt/interop/bin" >> "$GITHUB_PATH"
diff --git a/scripts/ci-test.sh b/scripts/ci-test.sh
index 1d7a7f9..af9dec6 100755
--- a/scripts/ci-test.sh
+++ b/scripts/ci-test.sh
@@ -92,7 +92,8 @@ run_step "cargo clippy (fast-deflate / zlib-ng)" cargo clippy \
 no_c_in_default_build() {
     local crate found=0
     for crate in clawhdf5-format clawhdf5-io clawhdf5-filters clawhdf5 \
-        clawhdf5-agent clawhdf5-ann clawhdf5-accel clawhdf5-netcdf4 clawhdf5-cli; do
+        clawhdf5-agent clawhdf5-ann clawhdf5-accel clawhdf5-netcdf4 clawhdf5-cli \
+        clawhdf5-tools; do
         local c_deps
         c_deps=$(cargo tree -q -p "$crate" -e normal,build --prefix none \
             | grep -E '^([a-z0-9_-]+-sys|cc|cmake) v' | sort -u)