diff --git a/libs/vkd3d-shader/spirv.c b/libs/vkd3d-shader/spirv.c
index 5d9b78b2..8a79c116 100644
--- a/libs/vkd3d-shader/spirv.c
+++ b/libs/vkd3d-shader/spirv.c
@@ -6892,11 +6892,11 @@ static enum GLSLstd450 spirv_compiler_map_ext_glsl_instruction(
 static void spirv_compiler_emit_ext_glsl_instruction(struct spirv_compiler *compiler,
         const struct vkd3d_shader_instruction *instruction)
 {
+    uint32_t instr_set_id, type_id, val_id, rev_val_id, uint_max_id, condition_id;
     struct vkd3d_spirv_builder *builder = &compiler->spirv_builder;
     const struct vkd3d_shader_dst_param *dst = instruction->dst;
     const struct vkd3d_shader_src_param *src = instruction->src;
     uint32_t src_id[SPIRV_MAX_SRC_COUNT];
-    uint32_t instr_set_id, type_id, val_id;
     unsigned int i, component_count;
     enum GLSLstd450 glsl_inst;
 
@@ -6925,8 +6925,12 @@ static void spirv_compiler_emit_ext_glsl_instruction(struct spirv_compiler *comp
     {
         /* In D3D bits are numbered from the most significant bit. */
         component_count = vsir_write_mask_component_count(dst->write_mask);
-        val_id = vkd3d_spirv_build_op_isub(builder, type_id,
+        uint_max_id = spirv_compiler_get_constant_uint_vector(compiler, UINT32_MAX, component_count);
+        condition_id = vkd3d_spirv_build_op_tr2(builder, &builder->function_stream, SpvOpIEqual,
+                vkd3d_spirv_get_type_id(builder, VKD3D_SHADER_COMPONENT_BOOL, component_count), val_id, uint_max_id);
+        rev_val_id = vkd3d_spirv_build_op_isub(builder, type_id,
                 spirv_compiler_get_constant_uint_vector(compiler, 31, component_count), val_id);
+        val_id = vkd3d_spirv_build_op_select(builder, type_id, condition_id, val_id, rev_val_id);
     }
 
     spirv_compiler_emit_store_dst(compiler, dst, val_id);
diff --git a/tests/d3d12.c b/tests/d3d12.c
index b17812b9..1fd07cca 100644
--- a/tests/d3d12.c
+++ b/tests/d3d12.c
@@ -10577,11 +10577,11 @@ static void test_shader_instructions(void)
 
         {&ps_bits_vector, {{{0x11111111, 0x00080000}}}, {{8,   1,  28,  19}}},
 
-        {&ps_firstbit_raw, {{{         0,          0}}}, {{ ~0u, ~0u, ~0u, 0}}, false, true},
+        {&ps_firstbit_raw, {{{         0,          0}}}, {{ ~0u, ~0u, ~0u, 0}}},
         {&ps_firstbit_raw, {{{0x80000000, 0x80000000}}}, {{  31,   0,   1, 0}}},
         {&ps_firstbit_raw, {{{0x80000001, 0x80000001}}}, {{   0,   0,   1, 0}}},
         {&ps_firstbit_raw, {{{0x11111111, 0x11111111}}}, {{   0,   3,   3, 0}}},
-        {&ps_firstbit_raw, {{{0x00080000, 0xffffffff}}}, {{  19,  12, ~0u, 0}}, false, true},
+        {&ps_firstbit_raw, {{{0x00080000, 0xffffffff}}}, {{  19,  12, ~0u, 0}}},
 
         {&ps_ishr, {{{0x00000000, 0x00000000, 0x00000000, 0x00000000}, {~0x1fu, 0, 32, 64}}},
                    {{0x00000000, 0x00000000, 0x00000000, 0x00000000}}},