diff --git a/charmcraft/extensions/gunicorn.py b/charmcraft/extensions/gunicorn.py
index 56ae3ce72..a2a76f773 100644
--- a/charmcraft/extensions/gunicorn.py
+++ b/charmcraft/extensions/gunicorn.py
@@ -163,6 +163,7 @@ def _get_root_snippet(self) -> dict[str, Any]:
                     "plugin": "charm",
                     "source": ".",
                     "build-snaps": ["rustup"],  # Needed to build pydantic.
+                    "override-build": "rustup default stable\ncraftctl default",
                 }
             },
         }
diff --git a/tests/extensions/test_gunicorn.py b/tests/extensions/test_gunicorn.py
index 1151fde37..54fcf638a 100644
--- a/tests/extensions/test_gunicorn.py
+++ b/tests/extensions/test_gunicorn.py
@@ -66,7 +66,12 @@ def flask_input_yaml_fixture():
                     "options": {**FlaskFramework.options, **FlaskFramework._WEBSERVER_OPTIONS}
                 },
                 "parts": {
-                    "charm": {"plugin": "charm", "source": ".", "build-snaps": ["rustup"]},
+                    "charm": {
+                        "plugin": "charm",
+                        "source": ".",
+                        "build-snaps": ["rustup"],
+                        "override-build": "rustup default stable\ncraftctl default",
+                    }
                 },
                 "peers": {"secret-storage": {"interface": "secret-storage"}},
                 "provides": {
@@ -120,7 +125,14 @@ def flask_input_yaml_fixture():
                 "config": {
                     "options": {**DjangoFramework.options, **DjangoFramework._WEBSERVER_OPTIONS}
                 },
-                "parts": {"charm": {"plugin": "charm", "source": ".", "build-snaps": ["rustup"]}},
+                "parts": {
+                    "charm": {
+                        "plugin": "charm",
+                        "source": ".",
+                        "build-snaps": ["rustup"],
+                        "override-build": "rustup default stable\ncraftctl default",
+                    }
+                },
                 "peers": {"secret-storage": {"interface": "secret-storage"}},
                 "provides": {
                     "metrics-endpoint": {"interface": "prometheus_scrape"},
@@ -258,4 +270,5 @@ def test_handle_charm_part(flask_input_yaml, tmp_path):
         "plugin": "charm",
         "source": ".",
         "build-snaps": ["rustup"],
+        "override-build": "rustup default stable\ncraftctl default",
     }
diff --git a/tests/spread/commands/init-flask-framework/task.yaml b/tests/spread/commands/init-flask-framework/task.yaml
index fd58ecbf6..4fdb20425 100644
--- a/tests/spread/commands/init-flask-framework/task.yaml
+++ b/tests/spread/commands/init-flask-framework/task.yaml
@@ -6,6 +6,12 @@ systems:
   - ubuntu-22.04-64
 
 execute: |
+  # Required for fetch-libs to succeed since the libraries are not available on
+  # the staging environment
+  unset CHARMCRAFT_STORE_API_URL
+  unset CHARMCRAFT_UPLOAD_URL
+  unset CHARMCRAFT_REGISTRY_URL
+
   mkdir -p test-init
   cd test-init
   charmcraft init --profile flask-framework