diff --git a/util/test/demos/d3d12/d3d12_draw_zoo.cpp b/util/test/demos/d3d12/d3d12_draw_zoo.cpp
index 834fdb26d..89781b012 100644
--- a/util/test/demos/d3d12/d3d12_draw_zoo.cpp
+++ b/util/test/demos/d3d12/d3d12_draw_zoo.cpp
@@ -219,8 +219,9 @@ float4 main(v2f IN) : SV_Target0
       vbData[i].col.y = float(i) / 200.0f;
     }
 
-    ID3D12ResourcePtr vb =
-        MakeBuffer().Data(vbData).Size(UINT((vbData.size() + 100) * sizeof(DefaultA2V)));
+    vbData.resize(vbData.size() + 100);
+
+    ID3D12ResourcePtr vb = MakeBuffer().Data(vbData).Size(UINT(vbData.size() * sizeof(DefaultA2V)));
 
     Vec4f instData[256] = {};
     for(int i = 0; i < ARRAY_COUNT(instData); i++)