diff --git a/libs/vkd3d-shader/msl.c b/libs/vkd3d-shader/msl.c
index f113721eb..cf01772ef 100644
--- a/libs/vkd3d-shader/msl.c
+++ b/libs/vkd3d-shader/msl.c
@@ -481,7 +481,7 @@ static enum msl_data_type msl_print_register_name(struct vkd3d_string_buffer *bu
                         "Internal compiler error: Unhandled sample coverage mask in shader type #%x.",
                         gen->program->shader_version.type);
             vkd3d_string_buffer_printf(buffer, "o_mask");
-            return MSL_DATA_FLOAT;
+            return MSL_DATA_UNION;
 
         default:
             msl_compiler_error(gen, VKD3D_SHADER_ERROR_MSL_INTERNAL,
@@ -1952,7 +1952,7 @@ static void msl_generate_entrypoint_epilogue(struct msl_generator *gen)
     }
 
     if (bitmap_is_set(gen->program->io_dcls, VKD3DSPR_SAMPLEMASK))
-        vkd3d_string_buffer_printf(gen->buffer, "    output.shader_out_mask = as_type<uint>(o_mask);\n");
+        vkd3d_string_buffer_printf(gen->buffer, "    output.shader_out_mask = o_mask.u;\n");
 }
 
 static void msl_generate_entrypoint(struct msl_generator *gen)
@@ -1999,7 +1999,7 @@ static void msl_generate_entrypoint(struct msl_generator *gen)
     vkd3d_string_buffer_printf(gen->buffer, "    vkd3d_vec4 %s_out[%u];\n", gen->prefix, 32);
     vkd3d_string_buffer_printf(gen->buffer, "    vkd3d_%s_out output;\n", gen->prefix);
     if (bitmap_is_set(gen->program->io_dcls, VKD3DSPR_SAMPLEMASK))
-        vkd3d_string_buffer_printf(gen->buffer, "    float o_mask;\n");
+        vkd3d_string_buffer_printf(gen->buffer, "    vkd3d_scalar o_mask;\n");
     vkd3d_string_buffer_printf(gen->buffer, "\n");
 
     msl_generate_entrypoint_prologue(gen);
@@ -2081,7 +2081,7 @@ static int msl_generator_generate(struct msl_generator *gen, struct vkd3d_shader
     if (bitmap_is_set(gen->program->io_dcls, VKD3DSPR_DEPTHOUT))
         vkd3d_string_buffer_printf(gen->buffer, ", thread float &o_depth");
     if (bitmap_is_set(gen->program->io_dcls, VKD3DSPR_SAMPLEMASK))
-        vkd3d_string_buffer_printf(gen->buffer, ", thread float &o_mask");
+        vkd3d_string_buffer_printf(gen->buffer, ", thread vkd3d_scalar &o_mask");
     if (gen->program->descriptors.descriptor_count)
         vkd3d_string_buffer_printf(gen->buffer, ", constant descriptor *descriptors");
     vkd3d_string_buffer_printf(gen->buffer, ")\n{\n");