diff --git a/htdocs/lib/Demodulator.js b/htdocs/lib/Demodulator.js
index 6761ccce..601bc86b 100644
--- a/htdocs/lib/Demodulator.js
+++ b/htdocs/lib/Demodulator.js
@@ -51,7 +51,7 @@ Envelope.prototype.draw = function(visible_range){
 
     var from = center_freq + this.demodulator.offset_frequency;
     var to = center_freq + this.demodulator.offset_frequency;
-    var fake_indicator = !this.demodulator.low_cut || !this.demodulator.high_cut;
+    var fake_indicator = typeof(this.demodulator.low_cut) !== 'number' || typeof(this.demodulator.high_cut) !== 'number';
     if (fake_indicator) {
         // fake values just so that the tuning indicator shows up
         var fixedBw = 100000