diff --git a/backend/device.impala b/backend/device.impala
index 19ed099..0b355ee 100644
--- a/backend/device.impala
+++ b/backend/device.impala
@@ -6,6 +6,7 @@ struct Device {
     alloc_mirror: fn(Buffer, i64) -> Buffer,
     transfer: fn(Buffer, Buffer) -> (),
     sqrt: fn(real_t) -> real_t,
+    real_floor: fn(real_t) -> real_t,
     loop_1d: fn(bool, i32, fn(i32) -> ()) -> (),
     add_iterator: fn(&mut i64) -> (),
     atomic_add_i32: fn(dev_i32_ptr, i32) -> i32
diff --git a/backend/mapping_cpu.impala b/backend/mapping_cpu.impala
index 6170e61..29232b7 100644
--- a/backend/mapping_cpu.impala
+++ b/backend/mapping_cpu.impala
@@ -10,6 +10,7 @@ fn @device() -> Device {
         alloc_mirror: |buf, size| { buf },
         transfer: |from, to| {},
         sqrt: @|a| { cpu_intrinsics.sqrt(a) },
+        real_floor: @|a| { cpu_intrinsics.floor(a) },
         loop_1d: @|vec, n, f| { vectorized_range(select(vec, get_vector_width(), 1), 0, n, |i, _| { f(i); }); },
         add_iterator: |iterator| { (*iterator)++; },
         atomic_add_i32: @|ptr, value| {
diff --git a/backend/mapping_gpu.impala b/backend/mapping_gpu.impala
index 113e658..37e150e 100644
--- a/backend/mapping_gpu.impala
+++ b/backend/mapping_gpu.impala
@@ -41,6 +41,7 @@ fn @device() -> Device {
         alloc_mirror: |buf, size| { alloc_cpu(size) },
         transfer: |from, to| { copy(from, to); },
         sqrt: @|a| { gpu_math.sqrt(a) },
+        real_floor: @|a| { gpu_math.floor(a) },
         loop_1d: loop_1d,
         add_iterator: |iterator| {},
         atomic_add_i32: @|ptr, value| { atomic_add_global_i32(ptr as &mut[1]i32, value) }
diff --git a/core/grid.impala b/core/grid.impala
index a4b4a9b..e14032a 100644
--- a/core/grid.impala
+++ b/core/grid.impala
@@ -404,9 +404,9 @@ fn get_resize(grid: Grid) -> i32 {
 }
 
 fn compute_cell_position(position: Vector3D, grid: Grid) -> [i32 * 3] {
-    let i = real_floor(((position.x - grid.aabb.xmin) / grid.spacing) as real_t) as i32;
-    let j = real_floor(((position.y - grid.aabb.ymin) / grid.spacing) as real_t) as i32;
-    let k = real_floor(((position.z - grid.aabb.zmin) / grid.spacing) as real_t) as i32;
+    let i = device().real_floor(((position.x - grid.aabb.xmin) / grid.spacing) as real_t) as i32;
+    let j = device().real_floor(((position.y - grid.aabb.ymin) / grid.spacing) as real_t) as i32;
+    let k = device().real_floor(((position.z - grid.aabb.zmin) / grid.spacing) as real_t) as i32;
     [i, j, k]
 }