diff --git a/xs/src/libslic3r/Fill/FillRectilinear2.cpp b/xs/src/libslic3r/Fill/FillRectilinear2.cpp
index e807a2164..58d9093af 100644
--- a/xs/src/libslic3r/Fill/FillRectilinear2.cpp
+++ b/xs/src/libslic3r/Fill/FillRectilinear2.cpp
@@ -1456,10 +1456,11 @@ Polylines FillCubic::fill_surface(const Surface *surface, const FillParams &para
     FillParams params2 = params;
     params2.density *= 0.333333333f;
     Polylines polylines_out;
-    if (! fill_surface_by_lines(surface, params2, 0.f, z, polylines_out) ||
-        ! fill_surface_by_lines(surface, params2, float(M_PI / 3.), -z, polylines_out) ||
+    coordf_t dx = sqrt(0.5) * z;
+    if (! fill_surface_by_lines(surface, params2, 0.f, dx, polylines_out) ||
+        ! fill_surface_by_lines(surface, params2, float(M_PI / 3.), - dx, polylines_out) ||
         // Rotated by PI*2/3 + PI to achieve reverse sloping wall.
-        ! fill_surface_by_lines(surface, params2, float(M_PI * 2. / 3.), z, polylines_out)) {
+        ! fill_surface_by_lines(surface, params2, float(M_PI * 2. / 3.), dx, polylines_out)) {
         printf("FillCubic::fill_surface() failed to fill a region.\n");
     } 
     return polylines_out; 
diff --git a/xs/src/libslic3r/Fill/FillRectilinear3.cpp b/xs/src/libslic3r/Fill/FillRectilinear3.cpp
index f4b198ade..1e7e3a1cd 100644
--- a/xs/src/libslic3r/Fill/FillRectilinear3.cpp
+++ b/xs/src/libslic3r/Fill/FillRectilinear3.cpp
@@ -1630,9 +1630,10 @@ Polylines FillCubic3::fill_surface(const Surface *surface, const FillParams &par
     params2.density *= 0.333333333f;
     Polylines polylines_out;
     std::vector<FillDirParams> fill_dir_params;
-    fill_dir_params.emplace_back(FillDirParams(this->spacing, 0.,             z));
-    fill_dir_params.emplace_back(FillDirParams(this->spacing, M_PI / 3.,     -z));
-    fill_dir_params.emplace_back(FillDirParams(this->spacing, 2. * M_PI / 3., z));
+    coordf_t dx = sqrt(0.5) * z;
+    fill_dir_params.emplace_back(FillDirParams(this->spacing, 0.,             dx));
+    fill_dir_params.emplace_back(FillDirParams(this->spacing, M_PI / 3.,     -dx));
+    fill_dir_params.emplace_back(FillDirParams(this->spacing, 2. * M_PI / 3., dx));
     if (! fill_surface_by_lines(surface, params2, fill_dir_params, polylines_out))
         printf("FillCubic3::fill_surface() failed to fill a region.\n");
     return polylines_out;