diff --git a/src/sprites/rendered-target.js b/src/sprites/rendered-target.js
index aa1963480..ae02b72bd 100644
--- a/src/sprites/rendered-target.js
+++ b/src/sprites/rendered-target.js
@@ -401,22 +401,16 @@ class RenderedTarget extends Target {
     /**
      * Add a costume, taking care to avoid duplicate names.
      * @param {!object} costumeObject Object representing the costume.
+     * @param {?int} index Index at which to add costume
      */
-    addCostume (costumeObject) {
+    addCostume (costumeObject, index) {
         const usedNames = this.sprite.costumes.map(costume => costume.name);
         costumeObject.name = StringUtil.unusedName(costumeObject.name, usedNames);
-        this.sprite.costumes.push(costumeObject);
-    }
-
-    /**
-     * Add a costume at the given index, taking care to avoid duplicate names.
-     * @param {!object} costumeObject Object representing the costume.
-     * @param {!int} index Index at which to add costume
-     */
-    addCostumeAt (costumeObject, index) {
-        const usedNames = this.sprite.costumes.map(costume => costume.name);
-        costumeObject.name = StringUtil.unusedName(costumeObject.name, usedNames);
-        this.sprite.costumes.splice(index, 0, costumeObject);
+        if (index) {
+            this.sprite.costumes.splice(index, 0, costumeObject);
+        } else {
+            this.sprite.costumes.push(costumeObject);
+        }
     }
 
     /**
@@ -472,22 +466,16 @@ class RenderedTarget extends Target {
     /**
      * Add a sound, taking care to avoid duplicate names.
      * @param {!object} soundObject Object representing the sound.
-     * @param {!int} index Index at which to add costume
+     * @param {?int} index Index at which to add costume
      */
-    addSoundAt (soundObject, index) {
+    addSound (soundObject, index) {
         const usedNames = this.sprite.sounds.map(sound => sound.name);
         soundObject.name = StringUtil.unusedName(soundObject.name, usedNames);
-        this.sprite.sounds.splice(index, 0, soundObject);
-    }
-
-    /**
-     * Add a sound, taking care to avoid duplicate names.
-     * @param {!object} soundObject Object representing the sound.
-     */
-    addSound (soundObject) {
-        const usedNames = this.sprite.sounds.map(sound => sound.name);
-        soundObject.name = StringUtil.unusedName(soundObject.name, usedNames);
-        this.sprite.sounds.push(soundObject);
+        if (index) {
+            this.sprite.sounds.splice(index, 0, soundObject);
+        } else {
+            this.sprite.sounds.push(soundObject);
+        }
     }
 
     /**
diff --git a/src/virtual-machine.js b/src/virtual-machine.js
index e2b18f2a3..f9fa45be3 100644
--- a/src/virtual-machine.js
+++ b/src/virtual-machine.js
@@ -337,7 +337,7 @@ class VirtualMachine extends EventEmitter {
         const clone = Object.assign({}, originalCostume);
         const md5ext = `${clone.assetId}.${clone.dataFormat}`;
         return loadCostume(md5ext, clone, this.runtime).then(() => {
-            this.editingTarget.addCostumeAt(clone, costumeIndex + 1);
+            this.editingTarget.addCostume(clone, costumeIndex + 1);
             this.editingTarget.setCostume(costumeIndex + 1);
             this.emitTargetsUpdate();
         });
@@ -352,7 +352,7 @@ class VirtualMachine extends EventEmitter {
         const originalSound = this.editingTarget.getSounds()[soundIndex];
         const clone = Object.assign({}, originalSound);
         return loadSound(clone, this.runtime).then(() => {
-            this.editingTarget.addSoundAt(clone, soundIndex + 1);
+            this.editingTarget.addSound(clone, soundIndex + 1);
             this.emitTargetsUpdate();
         });
     }