diff --git a/codegen/genfacet b/codegen/genfacet
index dc8b98a..baea989 100755
--- a/codegen/genfacet
+++ b/codegen/genfacet
@@ -67,12 +67,18 @@ def format_args_routing(args):
     names = [p['name'] for p in args]
     return ', '.join([f"O::data()"] + names[1:])
 
-def format_args_impl(args, drepr):
+def format_args_impl_const(args, drepr):
     """ Format argument names, for implementation (IFoo_DRepr)
     """
     names = [f"{p['type']} {p['name']}" for p in args]
     return ', '.join([f"const {drepr} & self"] + names[1:])
 
+def format_args_impl_nonconst(args, drepr):
+    """ Format argument names, for implementation (IFoo_DRepr)
+    """
+    names = [f"{p['type']} {p['name']}" for p in args]
+    return ', '.join([f"{drepr} & self"] + names[1:])
+
 
 def gen_facet(env,
               idl_fname,
@@ -480,7 +486,8 @@ def main():
     env.filters['argnamesnodata'] = format_arg_names_nodata
     env.filters['argsnodata'] = format_args_nodata
     env.filters['argrouting'] = format_args_routing
-    env.filters['argimpl'] = format_args_impl
+    env.filters['argimplconst'] = format_args_impl_const
+    env.filters['argimplnonconst'] = format_args_impl_nonconst
 
     if idl['mode'] == 'facet':
         gen_facet(env=env,
diff --git a/codegen/iface_facet_repr.cpp.j2 b/codegen/iface_facet_repr.cpp.j2
index ce3e87b..5249929 100644
--- a/codegen/iface_facet_repr.cpp.j2
+++ b/codegen/iface_facet_repr.cpp.j2
@@ -17,7 +17,7 @@ namespace {{repr_ns1}} {
     namespace {{repr_ns2}} {
         {% for md in const_methods %}
         auto
-        {{iface_facet_repr}}::{{md.name}}({{md.args | argimpl(data_repr)}}){{md | staticqual}} -> {{md.return_type}}
+        {{iface_facet_repr}}::{{md.name}}({{md.args | argimplconst(data_repr)}}){{md | staticqual}} -> {{md.return_type}}
         {
             {% if md.return_type == "void" %}
             self.{{md.name}}({{md.args | argnamesnodata}});
@@ -27,6 +27,17 @@ namespace {{repr_ns1}} {
         }
 
         {% endfor %}
+        {% for md in nonconst_methods %}
+        auto
+        {{iface_facet_repr}}::{{md.name}}({{md.args | argimplnonconst(data_repr)}}){{md | staticqual}} -> {{md.return_type}}
+        {
+            {% if md.return_type == "void" %}
+            self.{{md.name}}({{md.args | argnamesnodata}});
+            {% else %}
+            return self.{{md.name}}({{md.args | argnamesnodata}});
+            {% endif %}
+        }
+        {% endfor %}
 
     } /*namespace {{repr_ns2}}*/
 } /*namespace {{repr_ns1}}*/
diff --git a/codegen/iface_facet_repr.hpp.j2 b/codegen/iface_facet_repr.hpp.j2
index afbd717..55b7994 100644
--- a/codegen/iface_facet_repr.hpp.j2
+++ b/codegen/iface_facet_repr.hpp.j2
@@ -51,14 +51,16 @@ namespace {{repr_ns1}} {
             /** @defgroup {{repr_ns2}}-{{facet_name_lc}}-{{data_repr_lc}}-methods **/
             ///@{
             {% endif %}
+            // const methods
             {% for md in const_methods %}
             /** {{md.doc}} **/
-            static {{md.return_type}} {{md.name}}({{md.args | argimpl(data_repr)}}){{md | staticqual}};
+            static {{md.return_type}} {{md.name}}({{md.args | argimplconst(data_repr)}}){{md | staticqual}};
             {% endfor %}
 
-            {% for md in methods %}
+            // non-const methods
+            {% for md in nonconst_methods %}
             /** {{md.doc}} **/
-            static {{md.return_type}} {{md.name}}({{md.args | argimpl(data_repr)}}){{md | staticqual}};
+            static {{md.return_type}} {{md.name}}({{md.args | argimplnonconst(data_repr)}}){{md | staticqual}};
             {% endfor %}
             {% if using_dox %}
             ///@}