diff --git a/src/assembly/boundary/assemblers.rs b/src/assembly/boundary/assemblers.rs
index 4d5d9f33..7453a0c7 100644
--- a/src/assembly/boundary/assemblers.rs
+++ b/src/assembly/boundary/assemblers.rs
@@ -212,8 +212,8 @@ fn assemble_batch_singular<
         a.set_trial_cell(*trial_cell);
         a.assemble(&mut local_mat);
 
-        let test_dofs = test_space.cell_dofs(*test_cell).unwrap();
-        let trial_dofs = trial_space.cell_dofs(*trial_cell).unwrap();
+        let test_dofs = unsafe { test_space.cell_dofs_unchecked(*test_cell) };
+        let trial_dofs = unsafe { trial_space.cell_dofs_unchecked(*trial_cell) };
 
         for (trial_dof, col) in izip!(trial_dofs, local_mat.col_iter()) {
             for (test_dof, entry) in izip!(test_dofs, col.iter()) {
@@ -292,7 +292,7 @@ fn assemble_batch_nonadjacent<
 
     for trial_cell in trial_cells {
         a.set_trial_cell(*trial_cell);
-        let trial_dofs = trial_space.cell_dofs(*trial_cell).unwrap();
+        let trial_dofs = unsafe { trial_space.cell_dofs_unchecked(*trial_cell) };
         for (i, test_cell) in test_cells.iter().enumerate() {
             if neighbours(test_grid, trial_grid, *test_cell, *trial_cell) {
                 continue;
@@ -301,7 +301,7 @@ fn assemble_batch_nonadjacent<
             a.set_test_cell_from_index(i);
             a.assemble(&mut local_mat);
 
-            let test_dofs = test_space.cell_dofs(*test_cell).unwrap();
+            let test_dofs = unsafe { test_space.cell_dofs_unchecked(*test_cell) };
 
             for (trial_dof, col) in izip!(trial_dofs, local_mat.col_iter()) {
                 for (test_dof, entry) in izip!(test_dofs, col.iter()) {
@@ -384,8 +384,8 @@ fn assemble_batch_singular_correction<
 
         a.assemble(&mut local_mat);
 
-        let test_dofs = test_space.cell_dofs(*test_cell).unwrap();
-        let trial_dofs = trial_space.cell_dofs(*trial_cell).unwrap();
+        let test_dofs = unsafe { test_space.cell_dofs_unchecked(*test_cell) };
+        let trial_dofs = unsafe { trial_space.cell_dofs_unchecked(*trial_cell) };
 
         for (trial_dof, col) in izip!(trial_dofs, local_mat.col_iter()) {
             for (test_dof, entry) in izip!(test_dofs, col.iter()) {
diff --git a/src/function/function_space/parallel.rs b/src/function/function_space/parallel.rs
index f6bd11ce..c22becf1 100644
--- a/src/function/function_space/parallel.rs
+++ b/src/function/function_space/parallel.rs
@@ -55,6 +55,9 @@ impl<
     fn global_size(&self) -> usize {
         self.global_size
     }
+    unsafe fn cell_dofs_unchecked(&self, cell: usize) -> &[usize] {
+        self.serial_space.cell_dofs_unchecked(cell)
+    }
     fn cell_dofs(&self, cell: usize) -> Option<&[usize]> {
         self.serial_space.cell_dofs(cell)
     }
@@ -278,6 +281,9 @@ impl<
     fn global_size(&self) -> usize {
         self.local_space.global_size()
     }
+    unsafe fn cell_dofs_unchecked(&self, cell: usize) -> &[usize] {
+        self.local_space.cell_dofs_unchecked(cell)
+    }
     fn cell_dofs(&self, cell: usize) -> Option<&[usize]> {
         self.local_space.cell_dofs(cell)
     }
diff --git a/src/function/function_space/serial.rs b/src/function/function_space/serial.rs
index 76041767..a1d0312c 100644
--- a/src/function/function_space/serial.rs
+++ b/src/function/function_space/serial.rs
@@ -82,9 +82,12 @@ impl<
     fn global_size(&self) -> usize {
         self.size
     }
+    unsafe fn cell_dofs_unchecked(&self, cell: usize) -> &[usize] {
+        self.cell_dofs.get_unchecked(cell)
+    }
     fn cell_dofs(&self, cell: usize) -> Option<&[usize]> {
         if cell < self.cell_dofs.len() {
-            Some(&self.cell_dofs[cell])
+            Some(unsafe { self.cell_dofs_unchecked(cell) })
         } else {
             None
         }
diff --git a/src/traits/function.rs b/src/traits/function.rs
index 56a9f3ae..e167466c 100644
--- a/src/traits/function.rs
+++ b/src/traits/function.rs
@@ -41,6 +41,12 @@ pub trait FunctionSpace {
     /// Get the local DOF numbers associated with a cell
     fn cell_dofs(&self, cell: usize) -> Option<&[usize]>;
 
+    /// Get the local DOF numbers associated with a cell
+    ///
+    /// # Safety
+    /// The function uses unchecked array access
+    unsafe fn cell_dofs_unchecked(&self, cell: usize) -> &[usize];
+
     /// Compute a colouring of the cells so that no two cells that share an entity with DOFs associated with it are assigned the same colour
     fn cell_colouring(&self) -> HashMap<ReferenceCellType, Vec<Vec<usize>>>;