diff --git a/web/pgadmin/browser/server_groups/servers/databases/schemas/functions/__init__.py b/web/pgadmin/browser/server_groups/servers/databases/schemas/functions/__init__.py
index 571afd7ef01..80ba1787bd6 100644
--- a/web/pgadmin/browser/server_groups/servers/databases/schemas/functions/__init__.py
+++ b/web/pgadmin/browser/server_groups/servers/databases/schemas/functions/__init__.py
@@ -1035,7 +1035,7 @@ def _update_arguments_for_get_sql(data, old_data):
         :return:
         """
         if 'arguments' in data and len(data['arguments']) > 0:
-            for arg in data['arguments']['changed']:
+            for arg in data['arguments'].get('changed', []):
                 for old_arg in old_data['arguments']:
                     if arg['argid'] == old_arg['argid']:
                         old_arg.update(arg)
@@ -1194,6 +1194,21 @@ def _get_sql_for_edit_mode(self, data, parallel_dict, all_ids_dict,
                     data[arg]) > 0) or arg in data:
                 data['change_func'] = True
 
+        # PostgreSQL cannot add an input argument to an existing
+        # function/procedure via CREATE OR REPLACE: a changed argument
+        # list is a different signature, so PostgreSQL creates a new,
+        # separate overloaded routine instead of replacing this one.
+        # Reject such edits explicitly, rather than silently leaving an
+        # orphaned routine behind.
+        if 'arguments' in data and isinstance(data['arguments'], dict) \
+                and data['arguments'].get('added'):
+            return False, gettext(
+                "Adding a new argument to an existing function/procedure "
+                "is not supported, as PostgreSQL would create a separate, "
+                "overloaded routine rather than replacing this one. "
+                "Please create a new function/procedure instead."
+            ), ''
+
         # If Function Definition/Arguments are changed then merge old
         #  Arguments with changed ones for Create/Replace Function
         # SQL statement
diff --git a/web/pgadmin/browser/server_groups/servers/databases/schemas/functions/static/js/function.ui.js b/web/pgadmin/browser/server_groups/servers/databases/schemas/functions/static/js/function.ui.js
index c6f1b649441..1e57e9d92f8 100644
--- a/web/pgadmin/browser/server_groups/servers/databases/schemas/functions/static/js/function.ui.js
+++ b/web/pgadmin/browser/server_groups/servers/databases/schemas/functions/static/js/function.ui.js
@@ -304,16 +304,16 @@ export default class FunctionSchema extends BaseUISchema {
     },
     {
       id: 'arguments', label: gettext('Arguments'), cell: 'string',
-      group: gettext('Definition'), type: 'collection', canAdd: function(){
-        return obj.isNew();
-      },
+      group: gettext('Definition'), type: 'collection',
       canDelete: true, mode: ['create', 'edit'],
       columns: ['argtype', 'argmode', 'argname', 'argdefval'],
       schema : new DefaultArgumentSchema(this.node_info, this.fieldOptions.getTypes),
       disabled: obj.inCatalog(),
-      canDeleteRow: function() {
-        return obj.isNew();
-      },
+      // Existing (already saved) arguments cannot be removed here, as
+      // PostgreSQL has no way to drop an argument from a function via
+      // CREATE OR REPLACE. Only rows added in the current session (not
+      // yet saved) can be deleted.
+      canDeleteRow: (state) => (this.isNew(state)),
     },{
       id: 'prosrc', label: gettext('Code'), cell: 'text',
       type: 'sql', mode: ['properties', 'create', 'edit'],
diff --git a/web/pgadmin/browser/server_groups/servers/databases/schemas/functions/tests/test_function_get_msql.py b/web/pgadmin/browser/server_groups/servers/databases/schemas/functions/tests/test_function_get_msql.py
index d574f7d46a8..8902052b23f 100644
--- a/web/pgadmin/browser/server_groups/servers/databases/schemas/functions/tests/test_function_get_msql.py
+++ b/web/pgadmin/browser/server_groups/servers/databases/schemas/functions/tests/test_function_get_msql.py
@@ -142,6 +142,46 @@ class FunctionGetmsqlTestCase(BaseTestGenerator):
                 }
             )
         ),
+        (
+            'Fetch Function msql with newly added argument is rejected',
+            dict(
+                url='/browser/function/msql/',
+                is_positive_test=True,
+                mocking_required=False,
+                with_function_id=True,
+                is_mock_local_function=False,
+                test_data={
+                    "name": "Test Function",
+                    "funcowner": "",
+                    "pronamespace": 2200,
+                    "prorettypename": "character varying",
+                    "lanname": "sql",
+                    "prosrc": "select '1'",
+                    "probin": "$libdir/",
+                    "variables": [],
+                    "seclabels": [],
+                    "acl": [],
+                    # PostgreSQL cannot add an argument to an existing
+                    # function via CREATE OR REPLACE (it would create a
+                    # separate, overloaded routine instead), so this must
+                    # be rejected with a clear error rather than silently
+                    # producing SQL that orphans a routine.
+                    "arguments": json.dumps({
+                        "added": [{
+                            "argname": "new_arg",
+                            "argtype": "integer",
+                            "argmode": "IN",
+                            "argdefval": "1"
+                        }]
+                    })
+                },
+                mock_data={},
+                expected_data={
+                    "status_code": 500,
+                    "check_errormsg": "not supported"
+                }
+            ),
+        ),
         (
             'Fetch Function msql fetch properties not found',
             dict(
@@ -222,5 +262,11 @@ def _get_sql(self, **kwargs):
 
         self.assertEqual(response.status_code,
                          self.expected_data['status_code'])
+        if 'check_string' in self.expected_data:
+            self.assertIn(self.expected_data['check_string'],
+                          response.json['data'])
+        if 'check_errormsg' in self.expected_data:
+            self.assertIn(self.expected_data['check_errormsg'],
+                          response.json['errormsg'])
         # Disconnect the database
         database_utils.disconnect_database(self, self.server_id, self.db_id)