diff --git a/tests/firedrake/conftest.py b/tests/firedrake/conftest.py
index 695239b685..1fd9344dd6 100644
--- a/tests/firedrake/conftest.py
+++ b/tests/firedrake/conftest.py
@@ -9,6 +9,7 @@
 os.environ["FIREDRAKE_DISABLE_OPTIONS_LEFT"] = "1"
 
 import pytest
+from mpi4py import MPI
 from petsctools import get_external_packages
 from pyadjoint.tape import (
     annotate_tape, get_working_tape, set_working_tape,
@@ -256,3 +257,10 @@ def __exit__(self, exc_type, exc_val, traceback):
 def petsc_raises():
     # This function is needed because pytest does not support classes as fixtures.
     return _petsc_raises
+
+
+@pytest.fixture
+def garbage_cleanup():
+    """Fixture that runs the parallel garbage collector."""
+    yield
+    PETSc.garbage_cleanup(MPI.COMM_WORLD)
diff --git a/tests/firedrake/output/test_io_function.py b/tests/firedrake/output/test_io_function.py
index 0ea6812428..9169b7919a 100644
--- a/tests/firedrake/output/test_io_function.py
+++ b/tests/firedrake/output/test_io_function.py
@@ -16,6 +16,11 @@
 func_name = "f"
 
 
+@pytest.fixture(autouse=True)
+def autouse_garbage_cleanup(garbage_cleanup):
+    pass
+
+
 def _initialise_function(f, _f, method):
     if method == "project":
         getattr(f, method)(_f, solver_parameters={"ksp_type": "cg", "pc_type": "sor", "ksp_rtol": 1.e-16})
diff --git a/tests/firedrake/regression/test_covariance_operator.py b/tests/firedrake/regression/test_covariance_operator.py
index 4a5ab20257..3fce2c7df3 100644
--- a/tests/firedrake/regression/test_covariance_operator.py
+++ b/tests/firedrake/regression/test_covariance_operator.py
@@ -39,7 +39,7 @@ def rng():
 @pytest.mark.parametrize("family", ("CG", "DG"))
 @pytest.mark.parametrize("mesh_type", ("interval", "square"))
 @pytest.mark.parametrize("backend_type", (PyOP2NoiseBackend, PetscNoiseBackend), ids=("pyop2", "petsc"))
-def test_white_noise(family, degree, mesh_type, dim, backend_type, rng):
+def test_white_noise(family, degree, mesh_type, dim, backend_type, rng, garbage_cleanup):
     """Test that white noise generator converges to a mass matrix covariance.
     """