diff --git a/src/physics.F90 b/src/physics.F90
index 0b276c9fc6..4e94ea2261 100644
--- a/src/physics.F90
+++ b/src/physics.F90
@@ -142,7 +142,7 @@ contains
     case ('total')
       cutoff = prn() * material_xs % total
     case ('scatter')
-      cutoff = prn() * material_xs % total - material_xs % absorption
+      cutoff = prn() * (material_xs % total - material_xs % absorption)
     case ('fission')
       cutoff = prn() * material_xs % fission
     end select