diff --git a/Cargo.lock b/Cargo.lock
index 64b49ef..c4c09ef 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -29,6 +29,7 @@ version = "0.2.0"
 dependencies = [
  "either",
  "ordered-float",
+ "rustc-hash",
 ]
 
 [[package]]
@@ -39,3 +40,9 @@ checksum = "4a91171844676f8c7990ce64959210cd2eaef32c2612c50f9fae9f8aaa6065a6"
 dependencies = [
  "num-traits",
 ]
+
+[[package]]
+name = "rustc-hash"
+version = "2.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "583034fd73374156e66797ed8e5b0d5690409c9226b22d87cb7f19821c05d152"
diff --git a/Cargo.toml b/Cargo.toml
index 22ebe75..08dd734 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -8,3 +8,4 @@ rust-version = "1.80.1"
 [dependencies]
 either = "1.13.0"
 ordered-float = "4.2.2"
+rustc-hash = "2.0.0"
diff --git a/src/book.rs b/src/book.rs
index ed29fd5..68b6c65 100644
--- a/src/book.rs
+++ b/src/book.rs
@@ -1,8 +1,9 @@
 use either::Either;
 use ordered_float::OrderedFloat;
+use rustc_hash::FxHashMap as HashMap;
 use std::cell::Cell;
 use std::cmp::min;
-use std::collections::{BTreeMap, HashMap, VecDeque};
+use std::collections::{BTreeMap, VecDeque};
 use std::fmt;
 use std::rc::Rc;