diff --git a/test-linuxcnc-wasm-cmake-safe-probe.sh b/test-linuxcnc-wasm-cmake-safe-probe.sh
index adf5a17..8e28488 100755
--- a/test-linuxcnc-wasm-cmake-safe-probe.sh
+++ b/test-linuxcnc-wasm-cmake-safe-probe.sh
@@ -942,6 +942,15 @@ grep -Fx "src/emc/tooldata/tooldata_mmap.cc" <<<"$wasm_manifest_blocked" >/dev/n
 wasm_manifest_blocked_header=$(./list-linuxcnc-wasm-manifest-sources.sh "$manifest" blocked-header)
 grep -Fx "src/emc/rs274ngc/boost_pyenum_macros.hh" <<<"$wasm_manifest_blocked_header" >/dev/null
 unknown_manifest_filter_log=$(mktemp "${TMPDIR:-/tmp}/cnc_sim_unknown_wasm_manifest_filter.XXXXXX.log")
+if ./list-linuxcnc-wasm-manifest-sources.sh "$manifest" core,header >"$unknown_manifest_filter_log" 2>&1; then
+    echo "wasm manifest source lister accepted a compound filter" >&2
+    exit 1
+fi
+if ! grep -F "manifest source filter must be a manifest group name: core,header" "$unknown_manifest_filter_log" >/dev/null; then
+    echo "wasm manifest source lister did not report compound filters clearly" >&2
+    sed -n '1,20p' "$unknown_manifest_filter_log" >&2
+    exit 1
+fi
 if ./list-linuxcnc-wasm-manifest-sources.sh "$manifest" bogus >"$unknown_manifest_filter_log" 2>&1; then
     echo "wasm manifest source lister accepted unknown filter" >&2
     exit 1