diff --git a/flowermd/base/system.py b/flowermd/base/system.py
index cccfb8ef..234a60be 100644
--- a/flowermd/base/system.py
+++ b/flowermd/base/system.py
@@ -398,9 +398,9 @@ def _scale_charges(self):
         abs_charge = sum(abs(charges))
         if abs_charge != 0:
             for site in self.gmso_system.sites:
-                site.charge -= abs(site.charge if site.charge else 0) * (
-                    net_charge / abs_charge
-                )
+                site.charge -= abs(
+                    site.charge if site.charge else 0 * u.Unit("C")
+                ) * (net_charge / abs_charge)
 
     def to_gsd(self, file_name):
         """Write the system's `hoomd_snapshot` to a GSD file."""