diff --git a/openssh/libmapstack.jinja b/openssh/libmapstack.jinja
new file mode 100644
index 0000000..9ea212b
--- /dev/null
+++ b/openssh/libmapstack.jinja
@@ -0,0 +1,127 @@
+{#- -*- coding: utf-8 -*- #}
+{#- vim: ft=jinja #}
+
+{#- Get the `tplroot` from `tpldir` #}
+{%- set tplroot = tpldir.split("/")[0] %}
+
+{%- macro mapstack(
+      files,
+      defaults=None,
+      log_prefix="libmapstack: "
+    ) %}
+{#-
+    Load YAML files in the order of `files` and merge successively the
+    values with `defaults` if the file exists.
+
+    Parameters:
+      - `files`: list of files to load
+
+      - `defaults`: default values to start the merging, they are
+        considered built-ins
+
+      - `log_prefix`: prefix used in the log outputs, by default it is
+        `libmapstack: `
+
+    Each YAML file must conform to the following layout:
+      - a mandatory `values` key to store the configuration values
+
+      - two optional keys to configure the use of `salt.slsutil.merge`
+
+        - an optional `strategy` key to configure the merging strategy,
+          for example `strategy: 'recurse'`, the default is `smart`
+
+        - an optional `merge_lists` key to configure if lists should be
+          merged or overridden for the `recurse` and `overwrite`
+          strategies, for example `merge_lists: 'true'`
+#}
+{%-   set stack = defaults | default({"values": {} }, boolean=True) %}
+
+{%-   do salt["log.debug"](
+        log_prefix
+        ~ "built-in configuration:\n"
+        ~ {"values": defaults | traverse("values")}
+        | yaml(False)
+      ) %}
+
+{%-   for yaml_filename in files %}
+{%-     do salt["log.debug"](
+          log_prefix
+          ~ "load configuration values from "
+          ~ yaml_filename
+        ) %}
+
+{%-     load_yaml as yaml_values %}
+{%-       include yaml_filename ignore missing %}
+{%-     endload %}
+
+{%-     do salt["log.debug"](
+          log_prefix
+          ~ "loaded configuration values from "
+          ~ yaml_filename
+          ~ ":\n"
+          ~ yaml_values
+          | yaml(False)
+        ) %}
+
+{%-     if yaml_values %}
+{#-       Per YAML file `salt["slsutil.merge"]` options or use defaults #}
+{%-       set _strategy = yaml_values
+            | traverse(
+              "strategy",
+              defaults
+              | traverse(
+                "strategy",
+                "smart"
+              )
+            ) %}
+{%-       set _merge_lists = yaml_values
+            | traverse(
+              "merge_lists",
+              defaults
+              | traverse(
+                "merge_lists",
+                False
+              )
+            )
+            | to_bool %}
+
+{#-       Update only the `values`, the `salt["slsutil.merge"]` options are never updated #}
+{%-       do stack.update(
+            {
+              "values": salt["slsutil.merge"](
+                stack["values"],
+                yaml_values
+                | traverse("values", {}),
+                strategy=_strategy,
+                merge_lists=_merge_lists,
+              )
+            }
+          ) %}
+{%-       do salt["log.debug"](
+            log_prefix
+            ~ "merged configuration values from "
+            ~ yaml_filename
+            ~ ", merge: strategy='"
+            ~ _strategy
+            ~ "', merge_lists='"
+            ~ _merge_lists
+            ~ "':\n"
+            ~ {"values": stack["values"]}
+            | yaml(False)
+          ) %}
+{%-     endif %}
+
+{%-   endfor %}
+
+{%-   do salt["log.debug"](
+        log_prefix
+        ~ "final configuration values:\n"
+        ~ {"values": stack["values"]}
+        | yaml(False)
+      ) %}
+
+{#- Output stack as YAML, caller should use with something like #}
+{#- `{%- set config = flexible_config(prefix="foo") | load_yaml %}` #}
+{{ stack | yaml }}
+
+{%- endmacro %}
diff --git a/openssh/map.jinja b/openssh/map.jinja
index 3919d84..8280213 100644
--- a/openssh/map.jinja
+++ b/openssh/map.jinja
@@ -4,6 +4,7 @@
 {#- Get the `tplroot` from `tpldir` #}
 {%- set tplroot = tpldir.split("/")[0] %}
 {%- from tplroot ~ "/libmatchers.jinja" import parse_matchers, query_map %}
+{%- from tplroot ~ "/libmapstack.jinja" import mapstack %}
 
 {#- Where to lookup parameters source files #}
 {%- set map_sources_dir = tplroot ~ "/parameters" %}
@@ -19,65 +20,22 @@
       "C@" ~ tplroot,
       "Y:G@id",
     ] %}
-{%- do salt["log.debug"](
-      "map.jinja: built-in configuration sources:\n"
-      ~ {"values": {
-          "map_jinja": {"sources": map_sources}
-          }
-        }
-      | yaml(False)
-    ) %}
 
 {#- Allow centralised map.jinja configuration #}
-{%- set _global_map_filename = "parameters/map_jinja.yaml" %}
-{%- do salt["log.debug"](
-      "map.jinja: load global map.jinja values from "
-      ~ _global_map_filename
-    ) %}
-{%- load_yaml as global_map_settings %}
-{%-   include _global_map_filename ignore missing %}
-{%- endload %}
-
-{%- if global_map_settings %}
-{%-   do salt["log.debug"](
-        "map.jinja: configure sources from global map.jinja configuration "
-        ~ _global_map_filename
-        ~ ":\n"
-        ~ {"map_jinja": global_map_settings}
-        | yaml(False)
-      ) %}
-{%-   set map_sources = global_map_settings
-        | traverse(
-          "values:sources",
-          map_sources,
-      ) %}
-{%- endif %}
-
+{%- set _global_param_filename = "parameters/map_jinja.yaml" %}
 {#- Allow per formula map.jinja configuration #}
-{%- set _map_filename = map_sources_dir ~ "/map_jinja.yaml" %}
-{%- do salt["log.debug"](
-      "map.jinja: load per formula map.jinja values from "
-      ~ _map_filename
-    ) %}
-{%- load_yaml as map_settings %}
-{%-   include _map_filename ignore missing %}
-{%- endload %}
+{%- set _formula_param_filename = map_sources_dir ~ "/map_jinja.yaml" %}
 
-{%- if map_settings %}
-{%-   do salt["log.debug"](
-        "map.jinja: configure sources from formula map.jinja configuration "
-        ~ _map_filename
-        ~ ":\n"
-        ~ {"map_jinja": map_settings}
-        | yaml(False)
-      ) %}
-{%-   set map_sources = map_settings
-      | traverse(
-        "values:sources",
-        map_sources,
-      ) %}
-{%- endif %}
+{%- set _map_settings = mapstack(
+      files=[_global_param_filename, _formula_param_filename],
+      defaults={
+        "values": {"sources": map_sources}
+      },
+      log_prefix="map.jinja configuration: ",
+    )
+    | load_yaml %}
 
+{%- set map_sources = _map_settings | traverse("values:sources") %}
 {%- do salt["log.debug"](
       "map.jinja: load parameters from sources:\n"
       ~ map_sources
@@ -101,8 +59,7 @@
 {#- Make sure to track `map.jinja` configuration with `_mapdata` #}
 {%- do default_settings["values"].update(
       {
-        "map_jinja": map_settings
-        | traverse("values", {})
+        "map_jinja": _map_settings["values"]
       }
     ) %}