diff --git a/image_analysis/structure_refinement/RefinementMinimiser.h b/image_analysis/structure_refinement/RefinementMinimiser.h
index 42bb3afe1..82ac9e118 100644
--- a/image_analysis/structure_refinement/RefinementMinimiser.h
+++ b/image_analysis/structure_refinement/RefinementMinimiser.h
@@ -27,6 +27,7 @@ public:
     void Reset() {
         s_.clear();
         y_.clear();
+        sy_.clear();
     }
     // The estimated diagonal of the Hessian; every element > 0.
     void SetDiagonal(std::vector<double> h) { h_ = std::move(h); }
@@ -94,9 +95,11 @@ public:
             if (sy > 1e-10 * std::sqrt(Dot(s, s) * Dot(y, y))) {
                 s_.push_back(std::move(s));
                 y_.push_back(std::move(y));
+                sy_.push_back(sy);
                 if (s_.size() > memory_) {
                     s_.pop_front();
                     y_.pop_front();
+                    sy_.pop_front();
                 }
             }
             const double decrease = f - f_new;
@@ -124,7 +127,7 @@ private:
         const size_t n = g.size(), m = s_.size();
         std::vector<double> q = g, a(m), rho(m);
         for (size_t i = m; i-- > 0;) {
-            rho[i] = 1.0 / Dot(s_[i], y_[i]);
+            rho[i] = 1.0 / sy_[i];
             a[i] = rho[i] * Dot(s_[i], q);
             for (size_t k = 0; k < n; k++)
                 q[k] -= a[i] * y_[i][k];
@@ -134,7 +137,7 @@ private:
             double yhy = 0;
             for (size_t k = 0; k < n; k++)
                 yhy += y_[m - 1][k] * y_[m - 1][k] / h_[k];
-            gamma = Dot(s_[m - 1], y_[m - 1]) / yhy;
+            gamma = sy_[m - 1] / yhy;
         }
         for (size_t k = 0; k < n; k++)
             q[k] *= gamma / h_[k];
@@ -149,5 +152,6 @@ private:
 
     size_t memory_;
     std::deque<std::vector<double>> s_, y_;
+    std::deque<double> sy_;   // s.y of each pair, as taken when it was kept
     std::vector<double> h_;
 };
diff --git a/image_analysis/structure_refinement/RefinementXray.cpp b/image_analysis/structure_refinement/RefinementXray.cpp
index 1ce87e07d..3cf0506bb 100644
--- a/image_analysis/structure_refinement/RefinementXray.cpp
+++ b/image_analysis/structure_refinement/RefinementXray.cpp
@@ -282,7 +282,14 @@ gemmi::Grid<float> BulkSolventMask::MaskGrid(const gemmi::UnitCell &cell, const
     grid.unit_cell = cell;
     grid.spacegroup = &sg;
     const double spacing = std::max(std::min(d_min / 3.0, MASK_SPACING_MAX), std::cbrt(cell.volume / MASK_POINTS_MAX));
-    grid.set_size_from_spacing(spacing, gemmi::GridSizeRounding::Up);
+    // set_size_from_spacing()'s size, without allocating the values
+    const std::array<int, 3> n = gemmi::good_grid_size({{cell.a / spacing, cell.b / spacing, cell.c / spacing}},
+                                                       gemmi::GridSizeRounding::Up, &sg);
+    grid.nu = n[0];
+    grid.nv = n[1];
+    grid.nw = n[2];
+    grid.calculate_spacing();
+    grid.axis_order = gemmi::AxisOrder::XYZ;
     return grid;
 }
 
@@ -291,6 +298,7 @@ void BulkSolventMask::Fmask(const gemmi::Model &model, const std::vector<gemmi::
     if (orbit_leaders_.empty())   // at the first mask: a GPU engine's refinement never draws one here
         orbit_leaders_ = OrbitLeaders(grid_, nthreads_);
     gemmi::Grid<float> mask = grid_;
+    mask.data.resize(mask.point_count());
     PutMaskOnGrid(mask, model, orbit_leaders_, nthreads_);
     const gemmi::FPhiGrid<float> fm = MapToFPhi(mask);
     f.clear();