diff --git a/ament_package/template/package_level/local_setup.bat.in b/ament_package/template/package_level/local_setup.bat.in
index 9b83676..4bb2015 100644
--- a/ament_package/template/package_level/local_setup.bat.in
+++ b/ament_package/template/package_level/local_setup.bat.in
@@ -23,7 +23,7 @@ set "AMENT_CURRENT_PREFIX="
 goto:eof
 
 
-:: Append non-duplicate values to environment variables
+:: Append values to environment variables
 :: using semicolons as separators and avoiding leading separators.
 :: first argument: the name of the result variable
 :: second argument: the value
@@ -45,6 +45,37 @@ goto:eof
   )
 goto:eof
 
+:: Append non-duplicate values to environment variables
+:: using semicolons as separators and avoiding trailing separators.
+:: first argument: the name of the result variable
+:: second argument: the value
+:ament_append_unique_value
+  setlocal enabledelayedexpansion
+  :: arguments
+  set "listname=%~1"
+  set "value=%~2"
+  :: expand the list variable
+  set "list=!%listname%!"
+  :: check if the list contains the value
+  set "is_duplicate="
+  if "%list%" NEQ "" (
+    for %%v in ("%list:;=";"%") do (
+      if "%%~v" == "%value%" set "is_duplicate=1"
+    )
+  )
+  :: if it is not a duplicate append it
+  if "%is_duplicate%" == "" (
+    :: if not empty, append a semi-colon
+    if "!list!" NEQ "" set "list=!list!;"
+    :: append the value
+    set "list=!list!%value%"
+  )
+  endlocal & (
+    :: set result variable in parent scope
+    set "%~1=%list%"
+  )
+goto:eof
+
 :: Call the specified batch file and output the name when tracing is requested.
 :: first argument: the batch file
 :call_file
diff --git a/ament_package/template/package_level/local_setup.sh.in b/ament_package/template/package_level/local_setup.sh.in
index 28e12cf..60a8b16 100644
--- a/ament_package/template/package_level/local_setup.sh.in
+++ b/ament_package/template/package_level/local_setup.sh.in
@@ -42,6 +42,57 @@ ament_append_value() {
   unset _listname
 }
 
+# function to append non-duplicate values to environment variables
+# using colons as separators and avoiding leading separators
+ament_append_unique_value() {
+  # arguments
+  _listname=$1
+  _value=$2
+  #echo "listname $_listname"
+  #eval echo "list value \$$_listname"
+  #echo "value $_value"
+
+  # check if the list contains the value
+  eval _values=\$$_listname
+  _duplicate=
+  _ament_append_unique_value_IFS=$IFS
+  IFS=":"
+  if [ "$AMENT_SHELL" = "zsh" ]; then
+    ament_zsh_to_array _values
+  fi
+  for _item in $_values; do
+    # ignore empty strings
+    if [ -z "$_item" ]; then
+      continue
+    fi
+    if [ $_item = $_value ]; then
+      _duplicate=1
+    fi
+  done
+  unset _item
+
+  # append only non-duplicates
+  if [ -z "$_duplicate" ]; then
+    # avoid leading separator
+    if [ -z "$_values" ]; then
+      eval $_listname=\"$_value\"
+      #eval echo "set list \$$_listname"
+    else
+      # field separator must not be a colon
+      unset IFS
+      eval $_listname=\"\$$_listname:$_value\"
+      #eval echo "append list \$$_listname"
+    fi
+  fi
+  IFS=$_ament_append_unique_value_IFS
+  unset _ament_append_unique_value_IFS
+  unset _duplicate
+  unset _values
+
+  unset _value
+  unset _listname
+}
+
 # function to prepend non-duplicate values to environment variables
 # using colons as separators and avoiding trailing separators
 ament_prepend_unique_value() {