diff --git a/regalloc2-tool/src/main.rs b/regalloc2-tool/src/main.rs
index 1763456f..c224834b 100644
--- a/regalloc2-tool/src/main.rs
+++ b/regalloc2-tool/src/main.rs
@@ -2,8 +2,7 @@ use std::path::PathBuf;
 
 use clap::Parser;
 use regalloc2::{
-    checker::Checker, serialize::SerializableFunction, Block, Edit, Function, InstOrEdit, Output,
-    RegallocOptions,
+    checker::Checker, serialize::SerializableFunction, Algorithm, Block, Edit, Function, InstOrEdit, Output, RegallocOptions
 };
 
 #[derive(Parser)]
@@ -15,6 +14,24 @@ struct Args {
 
     /// Input file containing a bincode-encoded SerializedFunction.
     input: PathBuf,
+
+    /// Which register allocation algorithm to use.
+    algorithm: CliAlgorithm,
+}
+
+#[derive(Clone, Copy, Debug, clap::ValueEnum)]
+enum CliAlgorithm {
+    Ion,
+    Fastalloc,
+}
+
+impl From<CliAlgorithm> for Algorithm {
+    fn from(cli_algo: CliAlgorithm) -> Algorithm {
+        match cli_algo {
+            CliAlgorithm::Ion => Algorithm::Ion,
+            CliAlgorithm::Fastalloc => Algorithm::Fastalloc,
+        }
+    }
 }
 
 fn main() {
@@ -32,7 +49,7 @@ fn main() {
     let options = RegallocOptions {
         verbose_log: true,
         validate_ssa: true,
-        use_fastalloc: true,
+        algorithm: args.algorithm.into()
     };
     let output = match regalloc2::run(&function, function.machine_env(), &options) {
         Ok(output) => output,
diff --git a/src/lib.rs b/src/lib.rs
index 3b0c4c72..248d5a83 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -34,7 +34,7 @@ macro_rules! trace_enabled {
     };
 }
 
-use core::hash::BuildHasherDefault;
+use core::{default, hash::BuildHasherDefault};
 use std::iter::FromIterator;
 use rustc_hash::FxHasher;
 type FxHashMap<K, V> = hashbrown::HashMap<K, V, BuildHasherDefault<FxHasher>>;
@@ -1559,13 +1559,19 @@ pub fn run<F: Function>(
     env: &MachineEnv,
     options: &RegallocOptions,
 ) -> Result<Output, RegAllocError> {
-    if options.use_fastalloc {
-        fastalloc::run(func, env, options.verbose_log, options.validate_ssa)
-    } else {
-        ion::run(func, env, options.verbose_log, options.validate_ssa)
+    match options.algorithm {
+        Algorithm::Ion => ion::run(func, env, options.verbose_log, options.validate_ssa),
+        Algorithm::Fastalloc => fastalloc::run(func, env, options.verbose_log, options.validate_ssa)
     }
 }
 
+#[derive(Clone, Copy, Debug, Default)]
+pub enum Algorithm {
+    #[default]
+    Ion,
+    Fastalloc,
+}
+
 /// Options for allocation.
 #[derive(Clone, Copy, Debug, Default)]
 pub struct RegallocOptions {
@@ -1575,6 +1581,6 @@ pub struct RegallocOptions {
     /// Run the SSA validator before allocating registers.
     pub validate_ssa: bool,
 
-    /// Run the SSRA algorithm
-    pub use_fastalloc: bool,
+    /// The register allocation algorithm to be used.
+    pub algorithm: Algorithm,
 }