diff --git a/htdocs/openwebrx.js b/htdocs/openwebrx.js
index 39c58dc..d7f03bd 100644
--- a/htdocs/openwebrx.js
+++ b/htdocs/openwebrx.js
@@ -511,7 +511,7 @@ function resize_scale() {
 }
 
 function canvas_get_freq_offset(relativeX) {
-    var rel = (relativeX / canvases[0].clientWidth);
+    var rel = (relativeX / canvas_container.clientWidth);
     return Math.round((bandwidth * rel) - (bandwidth / 2));
 }