diff --git a/src/blocks/scratch3_looks.js b/src/blocks/scratch3_looks.js
index 6addc629..bd885dbf 100644
--- a/src/blocks/scratch3_looks.js
+++ b/src/blocks/scratch3_looks.js
@@ -353,7 +353,7 @@ class Scratch3LooksBlocks {
      */
     _setCostume (target, requestedCostume, optZeroIndex) {
         if (typeof requestedCostume === 'number') {
-            // Numbers should be treated as comments, always
+            // Numbers should be treated as costume indices, always
             target.setCostume(optZeroIndex ? requestedCostume : requestedCostume - 1);
         } else {
             const costumeIndex = target.getCostumeIndexByName(requestedCostume.toString());
@@ -386,16 +386,17 @@ class Scratch3LooksBlocks {
      */
     _setBackdrop (stage, requestedBackdrop, optZeroIndex) {
         if (typeof requestedBackdrop === 'number') {
+            // Numbers should be treated as backdrop indices, always
             stage.setCostume(optZeroIndex ? requestedBackdrop : requestedBackdrop - 1);
-        } else if (requestedBackdrop === 'next backdrop') {
-            stage.setCostume(stage.currentCostume + 1);
-        } else if (requestedBackdrop === 'previous backdrop') {
-            stage.setCostume(stage.currentCostume - 1);
         } else {
             const costumeIndex = stage.getCostumeIndexByName(requestedBackdrop.toString());
 
             if (costumeIndex !== -1) {
                 stage.setCostume(costumeIndex);
+            } else if (requestedBackdrop === 'next backdrop') {
+                stage.setCostume(stage.currentCostume + 1);
+            } else if (requestedBackdrop === 'previous backdrop') {
+                stage.setCostume(stage.currentCostume - 1);
             } else if (requestedBackdrop === 'random backdrop') {
                 const numCostumes = stage.getCostumes().length;
                 if (numCostumes > 1) {
diff --git a/test/unit/blocks_looks.js b/test/unit/blocks_looks.js
index ab0552a0..779f3610 100644
--- a/test/unit/blocks_looks.js
+++ b/test/unit/blocks_looks.js
@@ -129,9 +129,11 @@ test('switch backdrop block runs correctly', t => {
     t.strictEqual(testBackdrop(['a', 'b', 'c', 'd'], 'previous backdrop', 3), 2);
     t.strictEqual(testBackdrop(['a', 'b', 'c', 'd'], 'next backdrop', 2), 3);
 
-    // 'previous backdrop' and 'next backdrop' can't be overriden
-    t.strictEqual(testBackdrop(['a', 'previous backdrop', 'c', 'd'], 'previous backdrop', 4), 3);
-    t.strictEqual(testBackdrop(['next backdrop', 'b', 'c', 'd'], 'next backdrop'), 2);
+    // 'previous backdrop', 'previous backdrop', 'random backdrop' can be overriden
+    // Test is deterministic since 'random backdrop' will not pick the same backdrop as currently selected
+    t.strictEqual(testBackdrop(['a', 'previous backdrop', 'c', 'd'], 'previous backdrop', 4), 2);
+    t.strictEqual(testBackdrop(['next backdrop', 'b', 'c', 'd'], 'next backdrop', 3), 1);
+    t.strictEqual(testBackdrop(['random backdrop', 'b', 'c', 'd'], 'random backdrop'), 1);
 
     // NaN, Infinity, and true are the first costume
     t.strictEqual(testBackdrop(['a', 'b', 'c', 'd'], NaN, 2), 1);