diff --git a/.gitignore b/.gitignore
index 120764b..183bb88 100644
--- a/.gitignore
+++ b/.gitignore
@@ -166,3 +166,6 @@ cython_debug/
 
 # Rever
 rever/
+
+# VSCode
+.vscode
diff --git a/environment.yml b/environment.yml
index 3fd3d39..b7022a0 100644
--- a/environment.yml
+++ b/environment.yml
@@ -36,3 +36,4 @@ dependencies:
   - pip:
     - git+https://github.com/OpenFreeEnergy/openfe@main
     - git+https://github.com/OpenFreeEnergy/ofe-sphinx-theme@a45f3edd5bc3e973c1a01b577c71efa1b62a65d6
+    - git+https://github.com/openforcefield/openff-interchange@sltcap
diff --git a/src/pontibus/tests/utils/test_interchange_packmol.py b/src/pontibus/tests/utils/test_interchange_packmol.py
index 1cc5088..96dcd6b 100644
--- a/src/pontibus/tests/utils/test_interchange_packmol.py
+++ b/src/pontibus/tests/utils/test_interchange_packmol.py
@@ -1291,7 +1291,7 @@ def num_dih(self):
 
     @pytest.fixture(scope="class")
     def num_pos_ions(self):
-        return 8
+        return 7
 
     @pytest.fixture(scope="class")
     def num_neg_ions(self):
@@ -1358,7 +1358,6 @@ def test_solvent_nonbond_parameters(self, nonbonds, num_particles, num_waters):
                 assert from_openmm(e).m == pytest.approx(2.68724395648)
                 assert from_openmm(s).m_as(unit.angstroms) == pytest.approx(4.108824888)
 
-    @pytest.mark.xfail
     def test_system_total_charge(self, nonbonds, omm_system):
         total_charge = 0.0
         for i in range(omm_system.getNumParticles()):