diff --git a/src/scratch/ScratchObj.as b/src/scratch/ScratchObj.as
index 4313dee..3e99861 100644
--- a/src/scratch/ScratchObj.as
+++ b/src/scratch/ScratchObj.as
@@ -25,23 +25,23 @@
 
 package scratch {
 	import blocks.*;
-	
+
 	import filters.FilterPack;
-	
+
 	import flash.display.*;
 	import flash.events.MouseEvent;
 import flash.geom.ColorTransform;
 import flash.utils.*;
-	
+
 	import interpreter.*;
-	
+
 	import scratch.ScratchComment;
 import scratch.ScratchSprite;
 
 import translation.Translator;
-	
+
 	import util.*;
-	
+
 	import watchers.*;
 
 public class ScratchObj extends Sprite {
@@ -133,11 +133,19 @@ public class ScratchObj extends Sprite {
 	}
 
 	public function isCostumeNameUsed(name:String):Boolean {
-		var existingNames:Array = [];
+		name = name.toLowerCase();
 		for each (var c:ScratchCostume in costumes) {
-			existingNames.push(c.costumeName.toLowerCase());
+			if (c.costumeName.toLowerCase() == name) return true;
 		}
-		return (existingNames.indexOf(name.toLowerCase()) > -1);
+		return false;
+	}
+
+	public function isSoundNameUsed(name:String):Boolean {
+		name = name.toLowerCase();
+		for each (var s:ScratchSound in sounds) {
+			if (s.soundName.toLowerCase() == name) return true;
+		}
+		return false;
 	}
 
 	public function unusedCostumeName(baseName:String = ''):String {
diff --git a/src/scratch/ScratchRuntime.as b/src/scratch/ScratchRuntime.as
index 2b99651..29b9750 100644
--- a/src/scratch/ScratchRuntime.as
+++ b/src/scratch/ScratchRuntime.as
@@ -664,7 +664,7 @@ public class ScratchRuntime {
     public function renameSound(s:ScratchSound, newName:String):void {
         var obj:ScratchObj = app.viewedObj();
         var oldName:String = s.soundName;
-        if (obj.isCostumeNameUsed(newName)) return;
+        if (obj.isSoundNameUsed(newName)) return;
         s.soundName = newName;
         allUsesOfSoundDo(oldName, function (a:BlockArg):void {
             a.setArgValue(newName);