diff --git a/src/tree/mod.rs b/src/tree/mod.rs
index 25f3fb895..157a072f6 100644
--- a/src/tree/mod.rs
+++ b/src/tree/mod.rs
@@ -56,6 +56,8 @@ pub trait LayoutTree {
     fn compute_child_layout(&mut self, node_id: NodeId, inputs: LayoutInput) -> LayoutOutput;
 }
 
+/// A private trait which allows us to add extra convenience methods to types which implement
+/// LayoutTree without making those methods public.
 pub(crate) trait LayoutTreeExt: LayoutTree {
     /// Compute the size of the node given the specified constraints
     #[inline(always)]
diff --git a/src/tree/taffy_tree/tree.rs b/src/tree/taffy_tree/tree.rs
index f68147e9c..de4bdde90 100644
--- a/src/tree/taffy_tree/tree.rs
+++ b/src/tree/taffy_tree/tree.rs
@@ -161,11 +161,14 @@ where
                         inputs,
                         style,
                         Some(|known_dimensions, available_space| {
-                            (&mut self.measure_function)(known_dimensions, available_space, node, node_context)
+                            (self.measure_function)(known_dimensions, available_space, node, node_context)
                         }),
                     )
                 } else {
-                    let measure_function: Option<fn(Size<Option<f32>>, Size<AvailableSpace>) -> Size<f32>> = None;
+                    /// Type inference gets confused because we're just passing None here. So we give
+                    /// it a concrete type to work with (even though we never construct the inner type)
+                    type DummyMeasureFunction = Option<fn(Size<Option<f32>>, Size<AvailableSpace>) -> Size<f32>>;
+                    let measure_function: DummyMeasureFunction = None;
                     compute_leaf_layout(inputs, style, measure_function)
                 }
             }