diff --git a/Pmodules/bash b/Pmodules/bash
index 1adbc65..4b826b1 100644
--- a/Pmodules/bash
+++ b/Pmodules/bash
@@ -29,11 +29,9 @@ fi
 unset MODULE_VERSION
 unset MODULE_VERSION_STACK
 unset MODULESHOME
-#unset PMODULES_ENV
 
 declare -x PMODULES_DIR="${PMODULES_HOME}"
 
-
 #############################################################################
 # implement module comand as shell function
 #
@@ -44,9 +42,7 @@ module() {
 export -f module
 
 modbuild(){
-	(
-		"${PMODULES_HOME}/bin/modbuild" "$@"
-	)
+	"${PMODULES_HOME}/bin/modbuild" "$@"
 }
 export -f modbuild
 
diff --git a/Pmodules/libpbuild.bash b/Pmodules/libpbuild.bash
index 8b6030b..92b28ce 100644
--- a/Pmodules/libpbuild.bash
+++ b/Pmodules/libpbuild.bash
@@ -740,9 +740,8 @@ pbuild::make_all() {
 	#
 	set_full_module_name_and_prefix() {
 		do_simple_group(){
-			modulefile_dir=$(join_by '/' \
-						 "${ol_mod_root}/${GROUP}/${PMODULES_MODULEFILES_DIR}" \
-						 "${module_name}")
+			modulefile_dir="${ol_mod_root}/${GROUP}/${PMODULES_MODULEFILES_DIR}/"
+			modulefile_dir+="${module_name}"
 			modulefile_name="${modulefile_dir}/${module_version}"
 			PREFIX="${ol_inst_root}/${GROUP}/${module_name}/${module_version}"
 		}
@@ -783,7 +782,9 @@ pbuild::make_all() {
 			fi
 
 			modulefile_dir=$(join_by '/' \
-						 "${ol_mod_root}/${GROUP}/${PMODULES_MODULEFILES_DIR}" \
+						 "${ol_mod_root}" \
+						 "${GROUP}" \
+						 "${PMODULES_MODULEFILES_DIR}" \
 						 "${names[@]}" \
 						 "${module_name}")
 			modulefile_name="${modulefile_dir}/${module_version}"
diff --git a/Pmodules/libpmodules.bash.in b/Pmodules/libpmodules.bash.in
index ea15fbc..f394df5 100644
--- a/Pmodules/libpmodules.bash.in
+++ b/Pmodules/libpmodules.bash.in
@@ -43,7 +43,7 @@ compute_group_depth () {
 	test -d "${dir}" || return 1
         local group=${dir%/*}
         local group=${group##*/}
-	local -i result=$(${find} "${dir}" -depth \( -type f -o -type l \) \
+	result=$(${find} "${dir}" -depth \( -type f -o -type l \) \
                           -printf "%d" -quit 2>/dev/null)
 	(( result-=2 ))
 	# if a group doesn't contain a modulefile, depth is negativ
@@ -59,12 +59,14 @@ compute_group_depth () {
 #
 scan_groups () {
         local    ol
+	local depth
         for ol in "$@"; do
 		local mod_root="${OverlayInfo[${ol}:mod_root]}"
-		local -i depth
 	        local dir
 	        for dir in ${mod_root}/*/${PMODULES_MODULEFILES_DIR}; do
-			if [[ -n "${GroupDepths[${group}]}" ]]; then
+			local group="${dir%/*}"
+			group="${group##*/}"
+			if [[ ! -v GroupDepths[${group}] ]]; then
 				compute_group_depth depth "${dir}"
 				GroupDepths[$group]=${depth}
 			fi
diff --git a/Pmodules/modbuild.in b/Pmodules/modbuild.in
index ace74f8..c392ce9 100755
--- a/Pmodules/modbuild.in
+++ b/Pmodules/modbuild.in
@@ -489,6 +489,19 @@ build_modules_yaml(){
 		_result='base'
 	}
 
+	yaml_get_systems(){
+		local -n _result="$1"
+		local fname="$2"
+		local version="$3"
+		local idx="$4"
+		_result=$(yq -Ne e ".\"${version}\"[${idx}].systems" \
+			     "${fname}" 2>/dev/null)
+		(( $? == 0 )) && return
+		_result=$(yq -Ne e ".systems" "${fname}" 2>/dev/null)
+		(( $? == 0 )) && return
+		_result='any'
+	}
+
 	yaml_get_dependencies(){
 		local -n _result="$1"
 		local fname="$2"
@@ -519,16 +532,12 @@ build_modules_yaml(){
 	local m
 	local pattern="//"
 	for m in "${with_modules[@]}"; do
-                if [[ -n $(awk "/${m%/*}[\/ ]/" "${fname}") ]]; then
-		        pattern+=" && /${m//\//\\/}/"
-                fi
+		pattern+=" && /${m//\//\\/}/"
 	done
 
 	local -a versions
 	yaml_get_versions versions "${fname}" "${name}/${version}"
-	echo versions=${versions[@]}
 	for v in "${versions[@]}"; do
-		echo version=$v
 		local -i n_variants
 		yaml_get_num_variants n_variants "${fname}" "${v}"
 		local -i i
@@ -548,7 +557,21 @@ build_modules_yaml(){
 			yaml_get_dependencies deps "${fname}" "${v}" $i
 			ol_inst_root="${OverlayInfo[${ol_name}:inst_root]}"
 			ol_mod_root="${OverlayInfo[${ol_name}:mod_root]}"
-			
+
+			local systems
+			yaml_get_systems systems "${fname}" "${v}" $i
+			# build module if
+			# - systems is any
+			# - opt_system is listed in systems
+			local build_it='no'
+			if [[ "${systems}" == 'any' ]]; then
+				build_it='yes'
+			fi
+			if [[ ,${systems}, == *,${opt_system},* ]]; then
+				build_it='yes'
+			fi
+			[[ ${build_it} == 'no' ]] && continue
+
 			if (( ${#deps[@]} > 0 )); then
 				while read -a with_modules; do
 					pbuild.build_module \
diff --git a/Pmodules/modulecmd.bash.in b/Pmodules/modulecmd.bash.in
index 42e9471..133a8b8 100644
--- a/Pmodules/modulecmd.bash.in
+++ b/Pmodules/modulecmd.bash.in
@@ -1514,7 +1514,7 @@ subcommand_use() {
                 if [[ ! -v GroupDepths[${arg}] ]]; then
                         # this scan is required if a new group has been
                         # create inside an used overlay
-			scan_groups "${!OverlayInfo[@]}"
+			scan_groups "${UsedOverlays[@]}"
 			g_env_must_be_saved='yes'
                 fi
                 if [[ -n ${GroupDepths[${arg}]} ]]; then
@@ -2757,8 +2757,21 @@ if [[ -n ${PMODULES_ENV} ]]; then
 	eval "$("${base64}" -d <<< "${PMODULES_ENV}" 2>/dev/null)"
 fi
 if [[ -z ${Version} ]] || [[ ${Version} != ${PMODULES_VERSION} ]]; then
+	# this can only happen if the last command was
+	#   module load Pmodules/${PMODULES_VERSION}
+	#
+	# the values these two variables must be saved before initialising
+	declare _tmp_loaded_modules_="${LOADEDMODULES}"
+	declare _tmp_lmfiles_="${_LMFILES_}"
+
 	pmodules_init
-	#g_env_must_be_saved='yes'
+
+	# restore and export
+	LOADEDMODULES="${_tmp_loaded_modules_}"
+	_LMFILES_="${_tmp_lmfiles_}"
+        export_env \
+                LOADEDMODULES \
+                _LMFILES_
 fi
 
 if (( ${#GroupDepths[@]} == 0 )); then