diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index 37fdec4e..02f6d262 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -23,9 +23,9 @@ jobs:
           path: ~/.cache/pypoetry/virtualenvs
           key: ${{ runner.os }}-poetry-tests-${{ hashFiles('poetry.lock') }}
       - name: Install project
-        run: poetry install --no-interaction --sync --with=test
-      - name: Run tests
-        run: poetry run pytest
+        run: poetry install --no-interaction --sync --with=nox,test
+      - name: Run tests on Python ${{ matrix.python-version }}
+        run: poetry run nox --no-venv --no-install --non-interactive -s tests
 
   lint:
     strategy:
@@ -47,11 +47,9 @@ jobs:
           path: ~/.cache/pypoetry/virtualenvs
           key: ${{ runner.os }}-poetry-lint-${{ hashFiles('poetry.lock') }}
       - name: Install project
-        run: poetry install --no-interaction --sync --with=lint
-      - name: Run type-checking
-        run: poetry run mypy fawltydeps tests
-      - name: Run linter
-        run: poetry run pylint fawltydeps tests
+        run: poetry install --no-interaction --sync --no-root --only=nox,lint
+      - name: Run linters on Python ${{ matrix.python-version }}
+        run: poetry run nox --no-venv --no-install --non-interactive -s lint
 
   format:
     strategy:
@@ -73,11 +71,9 @@ jobs:
           path: ~/.cache/pypoetry/virtualenvs
           key: ${{ runner.os }}-poetry-format-${{ hashFiles('poetry.lock') }}
       - name: Install project
-        run: poetry install --no-interaction --sync --with=format
-      - name: Check formatting with Black
-        run: poetry run black . --check
-      - name: Run import sort checker
-        run: poetry run isort fawltydeps tests --check-only
+        run: poetry install --no-interaction --sync --no-root --only=nox,format
+      - name: Run formatting checks
+        run: poetry run nox --no-venv --no-install --non-interactive -s format
 
 # Inspiration for the CI setup:
 # https://github.com/marketplace/actions/python-poetry-action
diff --git a/noxfile.py b/noxfile.py
index ac3455d7..51c7bbd6 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -28,6 +28,14 @@ def install_groups(
     Auto-skip the `poetry export` step if the poetry.lock file is unchanged
     since the last time this session was run.
     """
+    if isinstance(session.virtualenv, nox.virtualenv.PassthroughEnv):
+        session.warn(
+            "Running outside a Nox virtualenv! We will skip installation here, "
+            "and simply assume that the necessary dependency groups have "
+            "already been installed by other means!"
+        )
+        return
+
     lockdata = Path("poetry.lock").read_bytes()
     digest = hashlib.blake2b(lockdata).hexdigest()
     requirements_txt = Path(session.cache_dir, session.name, "reqs_from_poetry.txt")