diff --git a/src/advance.cpp b/src/advance.cpp
index 962b25ea..4c79f548 100644
--- a/src/advance.cpp
+++ b/src/advance.cpp
@@ -93,14 +93,20 @@ bool advance(Planets &planet,
   if (didWork)
     didWork = neutralsMag.set_bcs(mGrid, time, indices);
 
+  // advect in the 3rd dimension (vertical), but only if we have it:
   if (gGrid.get_nAlts(false) > 1) {
     neutrals.advect_vertical(gGrid, time);
+    if (didWork & input.get_check_for_nans())
+      didWork = neutrals.check_for_nonfinites("After Vertical Neutral Advection");
     ions.advect_vertical(gGrid, time);
   }
 
-  //neutrals.exchange_old(gGrid);
-  //advect(gGrid, time, neutrals);
-
+  // advect in the 1st and 2nd dimensions (horizontal), but only if 
+  // we have those dimensions:
+  if (gGrid.get_HasXdim() || gGrid.get_HasYdim()) {
+    neutrals.exchange_old(gGrid);
+    advect(gGrid, time, neutrals);
+  }
   if (didWork & input.get_check_for_nans())
     didWork = neutrals.check_for_nonfinites("After Horizontal Advection");