diff --git a/lib/commands/thumbnail.js b/lib/commands/thumbnail.js
index 8342900..8630f84 100644
--- a/lib/commands/thumbnail.js
+++ b/lib/commands/thumbnail.js
@@ -31,7 +31,7 @@ exports.thumbnail = function thumbnail(options) {
                 throw new Error(utils.errorMessages['path']);
             }
 
-            if (options.width === undefined) {
+            if (options.width === undefined && options.height === undefined) {
                 throw new Error(utils.errorMessages['dim']);
             }