diff --git a/packages/mongodb-runner/README.md b/packages/mongodb-runner/README.md
index 17aef942..03954e19 100644
--- a/packages/mongodb-runner/README.md
+++ b/packages/mongodb-runner/README.md
@@ -37,6 +37,7 @@ Options:
       --version      MongoDB server version to use                      [string]
       --logDir       Directory to store server log files in             [string]
       --binDir       Directory containing mongod/mongos binaries        [string]
+      --downloadDir  Directory to store downloaded MongoDB versions in  [string]
       --tmpDir       Directory for temporary files    [string] [default: "/tmp"]
       --runnerDir    Directory for storing cluster metadata
                            [string] [default: "/home/addaleax/.mongodb/runner2"]
diff --git a/packages/mongodb-runner/src/cli.ts b/packages/mongodb-runner/src/cli.ts
index 0e7c23e2..6fdf2c6f 100644
--- a/packages/mongodb-runner/src/cli.ts
+++ b/packages/mongodb-runner/src/cli.ts
@@ -49,6 +49,11 @@ import * as utilities from './index';
       default: os.tmpdir(),
       describe: 'Directory for temporary files',
     })
+    .option('downloadDir', {
+      type: 'string',
+      describe:
+        'Directory for downloading and caching MongoDB binaries (uses tmpDir if not specified)',
+    })
     .option('runnerDir', {
       type: 'string',
       default: defaultRunnerDir,
diff --git a/packages/mongodb-runner/src/mongocluster.spec.ts b/packages/mongodb-runner/src/mongocluster.spec.ts
index 156b3ea7..9447a979 100644
--- a/packages/mongodb-runner/src/mongocluster.spec.ts
+++ b/packages/mongodb-runner/src/mongocluster.spec.ts
@@ -4,6 +4,7 @@ import { promises as fs } from 'fs';
 import path from 'path';
 import os from 'os';
 import createDebug from 'debug';
+import sinon from 'sinon';
 
 if (process.env.CI) {
   createDebug.enable('mongodb-runner,mongodb-downloader');
@@ -36,6 +37,39 @@ describe('MongoCluster', function () {
 
   afterEach(async function () {
     await cluster?.close();
+    sinon.restore();
+  });
+
+  it('can use custom downloadDir option for binary downloads', async function () {
+    const customDownloadDir = path.join(tmpDir, 'custom-downloads');
+
+    sinon
+      .stub(MongoCluster, 'downloadMongoDb' as any)
+      .resolves(customDownloadDir);
+
+    try {
+      cluster = await MongoCluster.start({
+        version: '6.x',
+        topology: 'standalone',
+        tmpDir,
+        downloadDir: customDownloadDir,
+        downloadOptions: {
+          platform: 'linux',
+          arch: 'x64',
+        },
+      });
+    } catch (err) {
+      // This will error because no actual binary gets downloaded
+    }
+
+    expect(MongoCluster['downloadMongoDb']).to.have.been.calledWith(
+      customDownloadDir,
+      '6.x',
+      {
+        platform: 'linux',
+        arch: 'x64',
+      },
+    );
   });
 
   it('can spawn a 6.x standalone mongod', async function () {
diff --git a/packages/mongodb-runner/src/mongocluster.ts b/packages/mongodb-runner/src/mongocluster.ts
index 406377f0..4d698087 100644
--- a/packages/mongodb-runner/src/mongocluster.ts
+++ b/packages/mongodb-runner/src/mongocluster.ts
@@ -17,6 +17,7 @@ export interface MongoClusterOptions
   secondaries?: number;
   shards?: number;
   version?: string;
+  downloadDir?: string;
   downloadOptions?: DownloadOptions;
 }
 
@@ -30,6 +31,14 @@ export class MongoCluster {
     /* see .start() */
   }
 
+  private static downloadMongoDb(
+    tmpdir: string,
+    targetVersionSemverSpecifier?: string | undefined,
+    options?: DownloadOptions | undefined,
+  ): Promise<string> {
+    return downloadMongoDb(tmpdir, targetVersionSemverSpecifier, options);
+  }
+
   serialize(): unknown /* JSON-serializable */ {
     return {
       topology: this.topology,
@@ -84,8 +93,8 @@ export class MongoCluster {
     const cluster = new MongoCluster();
     cluster.topology = options.topology;
     if (!options.binDir) {
-      options.binDir = await downloadMongoDb(
-        options.tmpDir,
+      options.binDir = await this.downloadMongoDb(
+        options.downloadDir ?? options.tmpDir,
         options.version,
         options.downloadOptions,
       );