diff --git a/list-linuxcnc-manifest-sources.sh b/list-linuxcnc-manifest-sources.sh
index b45a624..9b2c8dd 100755
--- a/list-linuxcnc-manifest-sources.sh
+++ b/list-linuxcnc-manifest-sources.sh
@@ -29,6 +29,11 @@ checks_duplicate_group() {
 LINUXCNC_ROOT="$linuxcnc_root" ./check-linuxcnc-inputs-cached.sh "$manifest"
 linuxcnc_root=$(cd "$linuxcnc_root" && pwd)
 
+if [[ "$filter_group" != "all" && ! "$filter_group" =~ ^[A-Za-z0-9_-]+$ ]]; then
+    echo "manifest source filter must be a manifest group name: $filter_group" >&2
+    exit 1
+fi
+
 if [[ "$filter_group" != "all" ]] && ! contains_group "$allowed_groups" "$filter_group"; then
     echo "unknown manifest source filter: $filter_group" >&2
     exit 1
diff --git a/test-all-native.sh b/test-all-native.sh
index d51de34..c386f5a 100755
--- a/test-all-native.sh
+++ b/test-all-native.sh
@@ -1171,6 +1171,15 @@ if grep -E '\.(hh|h)$' <<<"$native_manifest_core" >/dev/null; then
     echo "native manifest core compile group includes headers" >&2
     exit 1
 fi
+if ./list-linuxcnc-source-manifest-sources.sh "$manifest" core,header >"$unknown_filter_log" 2>&1; then
+    echo "native manifest source lister accepted a compound filter" >&2
+    exit 1
+fi
+if ! grep -F "manifest source filter must be a manifest group name: core,header" "$unknown_filter_log" >/dev/null; then
+    echo "native manifest source lister did not report compound filters clearly" >&2
+    sed -n '1,20p' "$unknown_filter_log" >&2
+    exit 1
+fi
 if ./list-linuxcnc-source-manifest-sources.sh "$manifest" bogus >"$unknown_filter_log" 2>&1; then
     echo "native manifest source lister accepted unknown filter" >&2
     exit 1
diff --git a/test-native.sh b/test-native.sh
index 773432e..82ec3c6 100755
--- a/test-native.sh
+++ b/test-native.sh
@@ -95,6 +95,7 @@ grep -F 'LinuxCNC source basis: the RS274 dump probe pairs LinuxCNC interpreter'
 grep -F 'LinuxCNC source basis: the bridge smoke source list is limited to the' list-linuxcnc-bridge-smoke-project-sources.sh >/dev/null
 grep -F 'LinuxCNC source basis: the RS274 API source list combines CMake-listed core' list-linuxcnc-rs274-api-project-sources.sh >/dev/null
 grep -F 'LinuxCNC source basis: manifest listers expose LinuxCNC-root relative source' list-linuxcnc-manifest-sources.sh >/dev/null
+grep -F 'manifest source filter must be a manifest group name: $filter_group' list-linuxcnc-manifest-sources.sh >/dev/null
 grep -F 'manifest source must be LinuxCNC-root relative: $path' list-linuxcnc-manifest-sources.sh >/dev/null
 grep -F 'LinuxCNC source basis: linuxcnc-rs274-source-files.txt enumerates the native' list-linuxcnc-source-manifest-sources.sh >/dev/null
 grep -F 'LinuxCNC source basis: linuxcnc-kinematics-source-files.txt tracks' list-linuxcnc-kinematics-manifest-sources.sh >/dev/null