diff --git a/compensation/forms/eco_account.py b/compensation/forms/eco_account.py
index 9e74e839..0352383c 100644
--- a/compensation/forms/eco_account.py
+++ b/compensation/forms/eco_account.py
@@ -175,7 +175,7 @@ class EditEcoAccountForm(NewEcoAccountForm):
     def is_valid(self):
         valid = super().is_valid()
 
-        deductable_surface = self.cleaned_data.get("surface")
+        deductable_surface = self.cleaned_data.get("surface") or 0.0
         deduction_surface_sum = self.instance.get_deductions_surface()
         if deductable_surface < deduction_surface_sum:
             self.add_error(