diff --git a/Source/TimeIntegration/ROMSX_uv3dmix.cpp b/Source/TimeIntegration/ROMSX_uv3dmix.cpp
index d92af3e6..35a4dc9e 100644
--- a/Source/TimeIntegration/ROMSX_uv3dmix.cpp
+++ b/Source/TimeIntegration/ROMSX_uv3dmix.cpp
@@ -23,6 +23,9 @@ ROMSX::uv3dmix  (const Box& bx,
 
     Box gbx2 = bx;
     gbx2.grow(IntVect(NGROW,NGROW,0));
+    // This might need to be done with a grown tilebox instead
+    Box gbx1 = bx;
+    gbx1.grow(IntVect(NGROW-1,NGROW-1,0));
     int ncomp = 1;
 
     FArrayBox fab_UFx(gbx2,1,amrex::The_Async_Arena());
@@ -48,7 +51,7 @@ ROMSX::uv3dmix  (const Box& bx,
     //DO j=JstrV-1,Jend
     //DO i=IstrU-1,Iend
     // Should these be on ubox/vbox?
-    amrex::ParallelFor(bx, ncomp,
+    amrex::ParallelFor(gbx1, ncomp,
             [=] AMREX_GPU_DEVICE (int i, int j, int k, int n)
             {
                 // cff depends on k, but UFx and VFe will only be affected by the last cell?
@@ -66,7 +69,7 @@ ROMSX::uv3dmix  (const Box& bx,
     //K_LOOP : DO k=1,N(ng)
     //DO j=Jstr,Jend+1
     //DO i=Istr,Iend+1
-    amrex::ParallelFor(bx, ncomp,
+    amrex::ParallelFor(gbx1, ncomp,
             [=] AMREX_GPU_DEVICE (int i, int j, int k, int n)
             {
                 //printf("%d %d %d %15.15g %15.15g %15.15g %15.15g\n",i,j,k,Hz(i-1,j,k),Hz(i,j,k),Hz(i-1,j-1,k),Hz(i,j-1,k));
@@ -90,7 +93,7 @@ ROMSX::uv3dmix  (const Box& bx,
     //K_LOOP : DO k=1,N(ng)
     //DO j=Jstr,Jend
     //DO i=IstrU,Iend
-    amrex::ParallelFor(bx, ncomp,
+    amrex::ParallelFor(gbx1, ncomp,
             [=] AMREX_GPU_DEVICE (int i, int j, int k, int n)
             {
                 const amrex::Real cff=dt_lev*0.25*(pm(i-1,j,0)+pm(i,j,0))*(pn(i-1,j,0)+pn(i,j,0));
@@ -112,7 +115,7 @@ ROMSX::uv3dmix  (const Box& bx,
     //K_LOOP : DO k=1,N(ng)
     //DO j=JstrV,Jend
     //DO i=Istr,Iend
-    amrex::ParallelFor(bx, ncomp,
+    amrex::ParallelFor(gbx1, ncomp,
             [=] AMREX_GPU_DEVICE (int i, int j, int k, int n)
             {
                 const amrex::Real cff=dt_lev*0.25*(pm(i,j,0)+pm(i,j-1,0))*(pn(i,j,0)+pn(i,j-1,0));