diff --git a/src/Ryujinx.Graphics.Shader/CodeGen/Msl/Declarations.cs b/src/Ryujinx.Graphics.Shader/CodeGen/Msl/Declarations.cs
index 09de9d0a2b..0b6aadd03b 100644
--- a/src/Ryujinx.Graphics.Shader/CodeGen/Msl/Declarations.cs
+++ b/src/Ryujinx.Graphics.Shader/CodeGen/Msl/Declarations.cs
@@ -75,6 +75,8 @@ namespace Ryujinx.Graphics.Shader.CodeGen.Msl
                 {
                     case ShaderStage.Vertex:
                         context.AppendLine("VertexOut out;");
+                        // TODO: Only add if necessary
+                        context.AppendLine("uint instance_index = instance_id + base_instance;");
                         break;
                     case ShaderStage.Fragment:
                         context.AppendLine("FragmentOut out;");
diff --git a/src/Ryujinx.Graphics.Shader/CodeGen/Msl/Instructions/IoMap.cs b/src/Ryujinx.Graphics.Shader/CodeGen/Msl/Instructions/IoMap.cs
index 38b9fff0df..f9d0a96d92 100644
--- a/src/Ryujinx.Graphics.Shader/CodeGen/Msl/Instructions/IoMap.cs
+++ b/src/Ryujinx.Graphics.Shader/CodeGen/Msl/Instructions/IoMap.cs
@@ -26,6 +26,7 @@ namespace Ryujinx.Graphics.Shader.CodeGen.Msl.Instructions
                 IoVariable.FrontFacing => ("in.front_facing", AggregateType.Bool),
                 IoVariable.GlobalId => ("thread_position_in_grid", AggregateType.Vector3 | AggregateType.U32),
                 IoVariable.InstanceId => ("instance_id", AggregateType.U32),
+                IoVariable.InstanceIndex => ("instance_index", AggregateType.U32),
                 IoVariable.InvocationId => ("INVOCATION_ID", AggregateType.S32),
                 IoVariable.PointCoord => ("point_coord", AggregateType.Vector2 | AggregateType.FP32),
                 IoVariable.PointSize => ("out.point_size", AggregateType.FP32),