diff --git a/README.md b/README.md
index 2a2461f..046e3f1 100644
--- a/README.md
+++ b/README.md
@@ -95,6 +95,7 @@ This cache is automatically keyed by:
 - the value of some compiler-specific environment variables (eg. RUSTFLAGS, etc), and
 - a hash of all `Cargo.lock` / `Cargo.toml` files found anywhere in the repository (if present).
 - a hash of all `rust-toolchain` / `rust-toolchain.toml` files in the root of the repository (if present).
+- a hash of installed packages as generated by `cargo install --list`.
 
 An additional input `key` can be provided if the builtin keys are not sufficient.
 
diff --git a/dist/restore/index.js b/dist/restore/index.js
index 6ea853e..8f78914 100644
--- a/dist/restore/index.js
+++ b/dist/restore/index.js
@@ -60055,6 +60055,9 @@ class CacheConfig {
             }
         }
         self.keyEnvs = keyEnvs;
+        // Installed packages and their versions are also considered for the key.
+        const packages = await getPackages();
+        hasher.update(packages);
         key += `-${hasher.digest("hex")}`;
         self.restoreKey = key;
         // Construct the lockfiles portion of the key:
@@ -60146,6 +60149,11 @@ async function getRustVersion() {
         .filter((s) => s.length === 2);
     return Object.fromEntries(splits);
 }
+async function getPackages() {
+    let stdout = await getCmdOutput("cargo", ["install", "--list"]);
+    // Make OS independent.
+    return stdout.split(/[\n\r]+/).join("\n");
+}
 async function globFiles(pattern) {
     const globber = await glob.create(pattern, {
         followSymbolicLinks: false,
diff --git a/dist/save/index.js b/dist/save/index.js
index 963ae45..4abea7f 100644
--- a/dist/save/index.js
+++ b/dist/save/index.js
@@ -60055,6 +60055,9 @@ class CacheConfig {
             }
         }
         self.keyEnvs = keyEnvs;
+        // Installed packages and their versions are also considered for the key.
+        const packages = await getPackages();
+        hasher.update(packages);
         key += `-${hasher.digest("hex")}`;
         self.restoreKey = key;
         // Construct the lockfiles portion of the key:
@@ -60146,6 +60149,11 @@ async function getRustVersion() {
         .filter((s) => s.length === 2);
     return Object.fromEntries(splits);
 }
+async function getPackages() {
+    let stdout = await getCmdOutput("cargo", ["install", "--list"]);
+    // Make OS independent.
+    return stdout.split(/[\n\r]+/).join("\n");
+}
 async function globFiles(pattern) {
     const globber = await glob.create(pattern, {
         followSymbolicLinks: false,
diff --git a/src/config.ts b/src/config.ts
index 4164037..962028f 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -103,6 +103,11 @@ export class CacheConfig {
     }
 
     self.keyEnvs = keyEnvs;
+
+    // Installed packages and their versions are also considered for the key.
+    const packages = await getPackages();
+    hasher.update(packages);
+
     key += `-${hasher.digest("hex")}`;
 
     self.restoreKey = key;
@@ -220,6 +225,12 @@ async function getRustVersion(): Promise<RustVersion> {
   return Object.fromEntries(splits);
 }
 
+async function getPackages(): Promise<string> {
+  let stdout = await getCmdOutput("cargo", ["install", "--list"]);
+  // Make OS independent.
+  return stdout.split(/[\n\r]+/).join("\n");
+}
+
 async function globFiles(pattern: string): Promise<string[]> {
   const globber = await glob.create(pattern, {
     followSymbolicLinks: false,