diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index b67fd11..4341cdc 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -16,7 +16,7 @@ jobs:
       matrix:
         toolchain:
           # Don't forget to update the README when bumping MSRV.
-          - 1.65.0
+          - 1.66.0
           - stable
           - beta
           - nightly
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8d497b1..fc1052f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,7 +1,7 @@
 ### v1.5.0 (unreleased)
 
 - **Changes**:
-    - Bump minimum supported Rust version to 1.65.0 (released 2022-11-03). This is for compatibility with new versions of some of rangemap's test dependencies.
+    - Bump minimum supported Rust version to 1.66.0 (released 2022-12-15). This is to gain access to `BTreeMap::first_key_value` and `BTreeMap::last_key_value`, and for compatibility with new versions of some of rangemap's test dependencies.
     - TODO: All of xfbs's PRs!
 
 ### v1.4.0 (2023-09-19)
diff --git a/Cargo.toml b/Cargo.toml
index 46f291a..5e51176 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -14,7 +14,7 @@ Map and set data structures whose keys are stored as ranges.
 Contiguous and overlapping ranges that map to the same value are coalesced into a single range.
 """
 categories = ["data-structures"]
-rust-version = "1.65.0"
+rust-version = "1.66.0"
 
 [dependencies]
 serde = { version = "1", optional = true }
diff --git a/README.md b/README.md
index ddec015..b10ba5e 100644
--- a/README.md
+++ b/README.md
@@ -3,7 +3,7 @@
 [![Crate](https://img.shields.io/crates/v/rangemap.svg)](https://crates.io/crates/rangemap)
 [![Docs](https://docs.rs/rangemap/badge.svg)](https://docs.rs/rangemap)
 [![Build status](https://github.com/jeffparsons/rangemap/workflows/CI/badge.svg)](https://github.com/jeffparsons/rangemap/actions)
-[![Rust](https://img.shields.io/badge/rust-1.65.0%2B-blue.svg?maxAge=3600)](https://github.com/jeffparsons/rangemap) <!-- Don't forget to update the GitHub actions config when bumping minimum Rust version. -->
+[![Rust](https://img.shields.io/badge/rust-1.66.0%2B-blue.svg?maxAge=3600)](https://github.com/jeffparsons/rangemap) <!-- Don't forget to update the GitHub actions config when bumping minimum Rust version. -->
 
 [`RangeMap`] and [`RangeInclusiveMap`] are map data structures whose keys
 are stored as ranges. Contiguous and overlapping ranges that map to the same