diff --git a/src/arena.rs b/src/arena.rs
index 4fc3e42..9124ab2 100644
--- a/src/arena.rs
+++ b/src/arena.rs
@@ -5,6 +5,7 @@ use alloc::vec::Vec;
 
 #[cfg(not(feature = "std"))]
 use core::{
+    mem,
     num::NonZeroUsize,
     ops::{Index, IndexMut},
 };
@@ -17,6 +18,7 @@ use serde::{Deserialize, Serialize};
 
 #[cfg(feature = "std")]
 use std::{
+    mem,
     num::NonZeroUsize,
     ops::{Index, IndexMut},
 };
@@ -79,18 +81,20 @@ impl<T> Arena<T> {
     /// assert_eq!(*arena[node_id].get(), "foo");
     /// ```
     pub fn get_node_id(&self, node: &Node<T>) -> Option<NodeId> {
-        // self.nodes.as_ptr_range() is not stable until rust 1.48
-        let start = self.nodes.as_ptr() as usize;
-        let end = start + self.nodes.len() * core::mem::size_of::<Node<T>>();
-        let p = node as *const Node<T> as usize;
-        if (start..end).contains(&p) {
-            let node_id = (p - start) / core::mem::size_of::<Node<T>>();
-            NonZeroUsize::new(node_id.wrapping_add(1)).map(|node_id_non_zero| {
-                NodeId::from_non_zero_usize(node_id_non_zero, self.nodes[node_id].stamp)
-            })
-        } else {
-            None
+        let nodes_range = self.nodes.as_ptr_range();
+        let p = node as *const Node<T>;
+
+        if !nodes_range.contains(&p) {
+            return None;
         }
+
+        let node_index = (p as usize - nodes_range.start as usize) / mem::size_of::<Node<T>>();
+        let node_id = NonZeroUsize::new(node_index.wrapping_add(1))?;
+
+        Some(NodeId::from_non_zero_usize(
+            node_id,
+            self.nodes[node_index].stamp,
+        ))
     }
 
     /// Retrieves the `NodeId` corresponding to the `Node` at `index` in the `Arena`, if it exists.