diff --git a/src/vpu-pdf-preview.js b/src/vpu-pdf-preview.js
index 426ca2d6b727771802d7fcd1ec85c439ddab8a1c..b096ad6bb000dcbb8e178aaa49a12a019d62042d 100644
--- a/src/vpu-pdf-preview.js
+++ b/src/vpu-pdf-preview.js
@@ -247,7 +247,8 @@ export class PdfPreview extends ScopedElementsMixin(VPULitElement) {
                         scaleY: scale,
                         angle: 0,
                         top: 0,
-                        left: 0
+                        left: 0,
+                        lockUniScaling: true  // lock aspect ratio when resizing
                     });
 
                     // we want to center the signature at the page