diff --git a/index.php b/index.php
index ba2d731..ee3962b 100644
--- a/index.php
+++ b/index.php
@@ -135,7 +135,7 @@
                     document.onmouseup = function() {
                         drawing = false;
                         // write image-bits for posting
-                        let canvasData = canvas.getImageData(0, 0, 128, 64);
+                        let canvasData = ctx.getImageData(0, 0, 128, 64);
                         bits.value = "";
 
                         // not best method, ideally want to create an array and then merge