diff --git a/components/layout/parallel.rs b/components/layout/parallel.rs
index 9e1009ce835..fcef3b54f98 100644
--- a/components/layout/parallel.rs
+++ b/components/layout/parallel.rs
@@ -10,7 +10,7 @@
 
 use context::{LayoutContext, SharedLayoutContext};
 use flow::{self, Flow, MutableFlowUtils, PostorderFlowTraversal, PreorderFlowTraversal};
-use flow_ref::{self, FlowRef};
+use flow_ref::FlowRef;
 use profile_traits::time::{self, TimerMetadata, profile};
 use std::mem;
 use std::sync::atomic::{AtomicIsize, Ordering};
@@ -220,7 +220,7 @@ fn assign_block_sizes_and_store_overflow(
 }
 
 pub fn traverse_flow_tree_preorder(
-        root: &mut FlowRef,
+        root: &mut Flow,
         profiler_metadata: Option<TimerMetadata>,
         time_profiler_chan: time::ProfilerChan,
         shared_layout_context: &SharedLayoutContext,
@@ -228,7 +228,7 @@ pub fn traverse_flow_tree_preorder(
     if opts::get().bubble_inline_sizes_separately {
         let layout_context = LayoutContext::new(shared_layout_context);
         let bubble_inline_sizes = BubbleISizes { layout_context: &layout_context };
-        flow_ref::deref_mut(root).traverse_postorder(&bubble_inline_sizes);
+        root.traverse_postorder(&bubble_inline_sizes);
     }
 
     run_queue_with_custom_work_data_type(queue, |queue| {
@@ -236,7 +236,7 @@ pub fn traverse_flow_tree_preorder(
                 time_profiler_chan, || {
             queue.push(WorkUnit {
                 fun: assign_inline_sizes,
-                data: (box vec![mut_owned_flow_to_unsafe_flow(root)], 0),
+                data: (box vec![borrowed_flow_to_unsafe_flow(root)], 0),
             })
         });
     }, shared_layout_context);
diff --git a/components/layout/sequential.rs b/components/layout/sequential.rs
index 804063b7629..5fca977b8b1 100644
--- a/components/layout/sequential.rs
+++ b/components/layout/sequential.rs
@@ -41,7 +41,7 @@ pub fn resolve_generated_content(root: &mut Flow, shared_layout_context: &Shared
     doit(root, 0, &mut traversal)
 }
 
-pub fn traverse_flow_tree_preorder(root: &mut FlowRef,
+pub fn traverse_flow_tree_preorder(root: &mut Flow,
                                    shared_layout_context: &SharedLayoutContext) {
     fn doit(flow: &mut Flow,
             assign_inline_sizes: AssignISizes,
@@ -61,8 +61,6 @@ pub fn traverse_flow_tree_preorder(root: &mut FlowRef,
 
     let layout_context = LayoutContext::new(shared_layout_context);
 
-    let root = flow_ref::deref_mut(root);
-
     if opts::get().bubble_inline_sizes_separately {
         let bubble_inline_sizes = BubbleISizes { layout_context: &layout_context };
         {
diff --git a/components/layout_thread/lib.rs b/components/layout_thread/lib.rs
index 2ff314d7170..c001f3b2345 100644
--- a/components/layout_thread/lib.rs
+++ b/components/layout_thread/lib.rs
@@ -875,7 +875,7 @@ impl LayoutThread {
     fn solve_constraints(layout_root: &mut FlowRef,
                          shared_layout_context: &SharedLayoutContext) {
         let _scope = layout_debug_scope!("solve_constraints");
-        sequential::traverse_flow_tree_preorder(layout_root, shared_layout_context);
+        sequential::traverse_flow_tree_preorder(flow_ref::deref_mut(layout_root), shared_layout_context);
     }
 
     /// Performs layout constraint solving in parallel.
@@ -892,7 +892,7 @@ impl LayoutThread {
 
         // NOTE: this currently computes borders, so any pruning should separate that
         // operation out.
-        parallel::traverse_flow_tree_preorder(layout_root,
+        parallel::traverse_flow_tree_preorder(flow_ref::deref_mut(layout_root),
                                               profiler_metadata,
                                               time_profiler_chan,
                                               shared_layout_context,