diff --git a/overhave/admin/views/testing_users.py b/overhave/admin/views/testing_users.py
index c32ea2da..880ba263 100644
--- a/overhave/admin/views/testing_users.py
+++ b/overhave/admin/views/testing_users.py
@@ -1,3 +1,4 @@
+from re import fullmatch
 from typing import cast
 
 from flask_admin.form import JSONField
@@ -50,6 +51,8 @@ class TestUserView(ModelViewConfigured):
 
     _feature_type: FeatureTypeName | None = None
 
+    _allowed_symbols = r"[a-zA-Z_]*"
+
     def on_form_prefill(self, form: Form, id) -> None:  # type: ignore  # noqa: A002
         if not isinstance(form._obj, db.TestUser):
             return
@@ -78,6 +81,8 @@ def _validate_json(model: db.TestUser) -> None:
                 raise ValidationError(f"Could not convert specified data into {parser.__name__} model!")
 
     def on_model_change(self, form: Form, model: db.TestUser, is_created: bool) -> None:
+        if model.key is not None and not fullmatch(self._allowed_symbols, model.key):
+            raise ValidationError("Key should contain only characters, digits or underscore!")
         self._feature_type = cast(FeatureTypeName, model.feature_type.name)
         self._validate_json(model)
         if is_created:
diff --git a/tests/unit/admin/test_testing_users.py b/tests/unit/admin/test_testing_users.py
index 42315fea..75179a89 100644
--- a/tests/unit/admin/test_testing_users.py
+++ b/tests/unit/admin/test_testing_users.py
@@ -47,6 +47,19 @@ def test_incorrect_model_raises_error(
         with pytest.raises(ValidationError):
             test_testing_user_view.on_model_change(form=form_mock, model=db_test_user, is_created=test_is_created)
 
+    @pytest.mark.parametrize("user_role", [db.Role.user, db.Role.admin], indirect=True)
+    @pytest.mark.parametrize("test_is_created", [False, True])
+    def test_key_with_spaces_for_model_raises_errors(
+        self,
+        test_testing_user_view: TestUserView,
+        current_user_mock: mock.MagicMock,
+        form_mock: mock.MagicMock,
+        test_is_created: bool,
+    ) -> None:
+        db_test_user = db.TestUser(key="kek kek")
+        with pytest.raises(ValidationError):
+            test_testing_user_view.on_model_change(form=form_mock, model=db_test_user, is_created=test_is_created)
+
     @pytest.mark.parametrize("user_role", [db.Role.admin, db.Role.user], indirect=True)
     def test_on_form_prefill_set_feature_type(
         self,