diff --git a/src/compiler/irgen.js b/src/compiler/irgen.js
index efecc28d..ea15d519 100644
--- a/src/compiler/irgen.js
+++ b/src/compiler/irgen.js
@@ -904,14 +904,8 @@ class ScriptTreeGenerator {
 
         case 'looks_changesizeby':
             return {
-                kind: 'looks.setSize',
-                size: {
-                    kind: 'op.add',
-                    left: {
-                        kind: 'looks.size'
-                    },
-                    right: this.descendInput(block, 'CHANGE')
-                }
+                kind: 'looks.changeSize',
+                size: this.descendInput(block, 'CHANGE')
             };
         case 'looks_cleargraphiceffects':
             return {
diff --git a/src/compiler/jsgen.js b/src/compiler/jsgen.js
index 6aa81ab2..75d2eb86 100644
--- a/src/compiler/jsgen.js
+++ b/src/compiler/jsgen.js
@@ -703,6 +703,9 @@ class JSGenerator {
         case 'looks.clearEffects':
             this.source += 'target.clearEffects();\n';
             break;
+        case 'looks.changeSize':
+            this.source += `target.setSize(target.size + ${this.descendInput(node.size).asNumber()});\n`;
+            break;
         case 'looks.forwardLayers':
             this.source += `target.goForwardLayers(${this.descendInput(node.layers).asNumber()});\n`;
             break;
diff --git a/test/fixtures/execute/tw-change-size-does-not-use-rounded-size.sb3 b/test/fixtures/execute/tw-change-size-does-not-use-rounded-size.sb3
new file mode 100644
index 00000000..dfffe493
Binary files /dev/null and b/test/fixtures/execute/tw-change-size-does-not-use-rounded-size.sb3 differ