diff --git a/NC Reactor Planner/Irradiator.cs b/NC Reactor Planner/Irradiator.cs
index 521c2ff..62bb026 100644
--- a/NC Reactor Planner/Irradiator.cs	
+++ b/NC Reactor Planner/Irradiator.cs	
@@ -66,7 +66,7 @@ private void WalkLineToValidSource(Vector3 offset)
                     Block block = Reactor.BlockAt(pos);
                     if (block is FuelCell fuelCell)
                     {
-                        if (fuelCell.Active)
+                        if (fuelCell.Active && moderatorsInLine >= 1)
                         {
                             this.ModeratedNeutronFlux += sumModeratorFlux;
                             fuelCell.PositionalEfficiency += sumModeratorEfficiency * EfficiencyMultiplier / moderatorsInLine;