diff --git a/npm/dist/WebAudioFontPlayer.js b/npm/dist/WebAudioFontPlayer.js
index 5e71ffc..4bfac97 100644
--- a/npm/dist/WebAudioFontPlayer.js
+++ b/npm/dist/WebAudioFontPlayer.js
@@ -296,10 +296,17 @@ function WebAudioFontPlayer() {
 		return envelope;
 	};
 	this.adjustPreset = function (audioContext, preset) {
-		for (var i = 0; i < preset.zones.length; i++) {
-			this.adjustZone(audioContext, preset.zones[i]);
-		}
-	};
+		const fixedZones = [];
+		for (let zone of preset.zones) {
+			if (zone.keyRangeLow > zone.keyRangeHigh) continue; // pathological case, not used anyway
+			fixedZones.push(zone);
+			this.adjustZone(audioContext, zone);
+		} //loop preset.zones
+		preset.zones = fixedZones;
+		// removing 1-semitone gaps between zones; important for microtones:
+		for (let index = 1; index < preset.zones.length; ++index)
+			preset.zones[index].keyRangeLow = preset.zones[index - 1].keyRangeHigh; 
+	};	
 	this.adjustZone = function (audioContext, zone) {
 		if (zone.buffer) {
 			//
diff --git a/npm/src/player.js b/npm/src/player.js
index 77fdc70..5e3e368 100644
--- a/npm/src/player.js
+++ b/npm/src/player.js
@@ -169,9 +169,16 @@ function WebAudioFontPlayer() {
 		return envelope;
 	};
 	this.adjustPreset = function (audioContext, preset) {
-		for (var i = 0; i < preset.zones.length; i++) {
-			this.adjustZone(audioContext, preset.zones[i]);
-		}
+		const fixedZones = [];
+		for (let zone of preset.zones) {
+			if (zone.keyRangeLow > zone.keyRangeHigh) continue; // pathological case, not used anyway
+			fixedZones.push(zone);
+			this.adjustZone(audioContext, zone);
+		} //loop preset.zones
+		preset.zones = fixedZones;
+		// removing 1-semitone gaps between zones; important for microtones:
+		for (let index = 1; index < preset.zones.length; ++index)
+			preset.zones[index].keyRangeLow = preset.zones[index - 1].keyRangeHigh; 
 	};
 	this.adjustZone = function (audioContext, zone) {
 		if (zone.buffer) {