diff --git a/CHANGELOG.md b/CHANGELOG.md
index e0ca679..2eb472d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.21.1] - 2022-04-12
+
+### Fixed
+- Fixed an issue introduced in v0.21.0 which prevented Docuum from working on Windows.
+
 ## [0.21.0] - 2022-04-05
 
 ### Added
diff --git a/Cargo.lock b/Cargo.lock
index b826ad3..32c0aea 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -171,7 +171,7 @@ dependencies = [
 
 [[package]]
 name = "docuum"
-version = "0.21.0"
+version = "0.21.1"
 dependencies = [
  "atty",
  "byte-unit",
diff --git a/Cargo.toml b/Cargo.toml
index 610546d..03c79f4 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "docuum"
-version = "0.21.0"
+version = "0.21.1"
 authors = ["Stephan Boyer <stephan@stephanboyer.com>"]
 edition = "2021"
 description = "LRU eviction of Docker images."
@@ -23,6 +23,8 @@ serde_json = "1.0"
 serde_yaml = "0.8"
 tempfile = "3"
 regex = "1.5.4"
+
+[target.'cfg(target_os = "linux")'.dependencies]
 sysinfo = "0.23.5"
 
 [dependencies.clap]
diff --git a/src/main.rs b/src/main.rs
index 5c9e3c3..0dd3bf4 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -41,11 +41,14 @@ const KEEP_OPTION: &str = "keep";
 #[derive(Copy, Clone)]
 enum Threshold {
     Absolute(Byte),
+
+    #[cfg(target_os = "linux")]
     Percentage(f64),
 }
 
 impl Threshold {
     // Parse a `Threshold`. Relative thresholds are only supported on Linux.
+    #[cfg(target_os = "linux")]
     fn from_str(threshold: &str) -> io::Result<Threshold> {
         match threshold.strip_suffix('%') {
             Some(threshold) => {
@@ -87,6 +90,18 @@ impl Threshold {
                 .map(Threshold::Absolute),
         }
     }
+
+    #[cfg(not(target_os = "linux"))]
+    fn from_str(threshold: &str) -> io::Result<Threshold> {
+        Byte::from_str(threshold)
+            .map_err(|_| {
+                io::Error::new(
+                    io::ErrorKind::InvalidInput,
+                    format!("Invalid absolute threshold {}.", threshold.code_str()),
+                )
+            })
+            .map(Threshold::Absolute)
+    }
 }
 
 // This struct represents the command-line arguments.
diff --git a/src/run.rs b/src/run.rs
index 6324c8b..74368c6 100644
--- a/src/run.rs
+++ b/src/run.rs
@@ -15,10 +15,14 @@ use {
         io::{self, BufRead, BufReader},
         mem::drop,
         ops::Deref,
-        path::{Path, PathBuf},
         process::{Command, Stdio},
         time::{Duration, SystemTime, UNIX_EPOCH},
     },
+};
+
+#[cfg(target_os = "linux")]
+use {
+    std::path::{Path, PathBuf},
     sysinfo::{Disk, DiskExt, RefreshKind, System, SystemExt},
 };
 
@@ -306,6 +310,7 @@ fn image_ids_in_use() -> io::Result<HashSet<String>> {
 }
 
 // Determine Docker's root directory.
+#[cfg(target_os = "linux")]
 fn docker_root_dir() -> io::Result<PathBuf> {
     // Query Docker for it.
     let output = Command::new("docker")
@@ -328,6 +333,7 @@ fn docker_root_dir() -> io::Result<PathBuf> {
 }
 
 // Find the disk containing a path.
+#[cfg(target_os = "linux")]
 fn get_disk_by_file<'a>(disks: &'a [Disk], path: &Path) -> io::Result<&'a Disk> {
     disks
         .iter()
@@ -345,6 +351,7 @@ fn get_disk_by_file<'a>(disks: &'a [Disk], path: &Path) -> io::Result<&'a Disk>
 }
 
 // Find size of filesystem on which docker root directory is stored.
+#[cfg(target_os = "linux")]
 fn docker_root_dir_filesystem_size() -> io::Result<Byte> {
     let root_dir = docker_root_dir()?;
     let system = System::new_with_specifics(RefreshKind::new().with_disks_list());
@@ -726,6 +733,8 @@ pub fn run(settings: &Settings, state: &mut State, first_run: &mut bool) -> io::
     // Determine the threshold in bytes.
     let threshold = match settings.threshold {
         Threshold::Absolute(b) => b,
+
+        #[cfg(target_os = "linux")]
         Threshold::Percentage(p) =>
         {
             #[allow(