diff --git a/src/pymatgen/core/composition.py b/src/pymatgen/core/composition.py
index 8eaa6a5400d..9d889d83780 100644
--- a/src/pymatgen/core/composition.py
+++ b/src/pymatgen/core/composition.py
@@ -487,7 +487,7 @@ def chemical_system(self) -> str:
         sorted alphabetically and joined by dashes, by convention for use
         in database keys.
         """
-        return "-".join(sorted(el.symbol for el in self.elements))
+        return "-".join(sorted(self.chemical_system_set))
 
     @property
     def num_atoms(self) -> float:
diff --git a/tests/core/test_composition.py b/tests/core/test_composition.py
index 1cf2c688e31..7c9b4dcdd33 100644
--- a/tests/core/test_composition.py
+++ b/tests/core/test_composition.py
@@ -701,6 +701,7 @@ def test_elements(self):
     def test_chemical_system(self):
         assert Composition({"Na": 1, "Cl": 1}).chemical_system == "Cl-Na"
         assert Composition({"Na+": 1, "Cl-": 1}).chemical_system == "Cl-Na"
+        assert Composition({"Na+": 1, "Na2+": 1, "Cl-": 1}).chemical_system == "Cl-Na"
 
     def test_chemical_system_set(self):
         assert Composition({"Na": 1, "Cl": 1}).chemical_system_set == {"Cl", "Na"}