diff --git a/lib/cli/writer.js b/lib/cli/writer.js
index 164a0a41..f8a966bd 100644
--- a/lib/cli/writer.js
+++ b/lib/cli/writer.js
@@ -25,6 +25,13 @@ const imageStream = require('../image-stream');
 const errors = require('../shared/errors');
 const constraints = require('../shared/drive-constraints');
 
+/**
+ * @summary Timeout, in milliseconds, to wait before unmounting on success
+ * @constant
+ * @type {Number}
+ */
+const UNMOUNT_ON_SUCCESS_TIMEOUT_MS = 2000;
+
 /**
  * @summary Write an image to a disk drive
  * @function
@@ -108,7 +115,14 @@ exports.writeImage = (imagePath, drive, options, onProgress) => {
           return Bluebird.resolve();
         }
 
-        return mountutils.unmountDiskAsync(drive.device);
+        // Closing a file descriptor on a drive containing mountable
+        // partitions causes macOS to mount the drive. If we try to
+        // unmount to quickly, then the drive might get re-mounted
+        // right afterwards.
+        return Bluebird.delay(UNMOUNT_ON_SUCCESS_TIMEOUT_MS)
+          .return(drive.device)
+          .then(mountutils.unmountDiskAsync);
+
       });
     });
   });