diff --git a/src/Ryujinx.Graphics.Shader/CodeGen/Msl/Declarations.cs b/src/Ryujinx.Graphics.Shader/CodeGen/Msl/Declarations.cs
index 1832ea146..912b162d2 100644
--- a/src/Ryujinx.Graphics.Shader/CodeGen/Msl/Declarations.cs
+++ b/src/Ryujinx.Graphics.Shader/CodeGen/Msl/Declarations.cs
@@ -392,6 +392,7 @@ namespace Ryujinx.Graphics.Shader.CodeGen.Msl
                 context.AppendLine("float4 position [[position, invariant]];");
                 context.AppendLine("bool front_facing [[front_facing]];");
                 context.AppendLine("float2 point_coord [[point_coord]];");
+                context.AppendLine("uint primitive_id [[primitive_id]];");
             }
 
             if (context.Definitions.IaIndexing)
diff --git a/src/Ryujinx.Graphics.Shader/CodeGen/Msl/Instructions/IoMap.cs b/src/Ryujinx.Graphics.Shader/CodeGen/Msl/Instructions/IoMap.cs
index 57c180fb4..e02d0a61f 100644
--- a/src/Ryujinx.Graphics.Shader/CodeGen/Msl/Instructions/IoMap.cs
+++ b/src/Ryujinx.Graphics.Shader/CodeGen/Msl/Instructions/IoMap.cs
@@ -31,7 +31,7 @@ namespace Ryujinx.Graphics.Shader.CodeGen.Msl.Instructions
                 IoVariable.PointCoord => ("in.point_coord", AggregateType.Vector2 | AggregateType.FP32),
                 IoVariable.PointSize => ("out.point_size", AggregateType.FP32),
                 IoVariable.Position => ("out.position", AggregateType.Vector4 | AggregateType.FP32),
-                IoVariable.PrimitiveId => ("primitive_id", AggregateType.S32),
+                IoVariable.PrimitiveId => ("in.primitive_id", AggregateType.U32),
                 IoVariable.SubgroupEqMask => ("thread_index_in_simdgroup >= 32 ? uint4(0, (1 << (thread_index_in_simdgroup - 32)), uint2(0)) : uint4(1 << thread_index_in_simdgroup, uint3(0))", AggregateType.Vector4 | AggregateType.U32),
                 IoVariable.SubgroupGeMask => ("uint4(insert_bits(0u, 0xFFFFFFFF, thread_index_in_simdgroup, 32 - thread_index_in_simdgroup), uint3(0)) & (uint4((uint)((simd_vote::vote_t)simd_ballot(true) & 0xFFFFFFFF), (uint)(((simd_vote::vote_t)simd_ballot(true) >> 32) & 0xFFFFFFFF), 0, 0))", AggregateType.Vector4 | AggregateType.U32),
                 IoVariable.SubgroupGtMask => ("uint4(insert_bits(0u, 0xFFFFFFFF, thread_index_in_simdgroup + 1, 32 - thread_index_in_simdgroup - 1), uint3(0)) & (uint4((uint)((simd_vote::vote_t)simd_ballot(true) & 0xFFFFFFFF), (uint)(((simd_vote::vote_t)simd_ballot(true) >> 32) & 0xFFFFFFFF), 0, 0))", AggregateType.Vector4 | AggregateType.U32),