diff --git a/src/gray.f b/src/gray.f
index 7b4b44e..c32421d 100644
--- a/src/gray.f
+++ b/src/gray.f
@@ -1349,8 +1349,8 @@ c          end do
 c
 c     compute max and min z of last closed surface
 c
-      rbmin=rax
-      rbmax=rax
+      rbmin=rmaxis
+      rbmax=rmaxis
       if (nbbbs.gt.1) then
         zbmin=1.0d+30
         zbmax=-1.0d+30