diff --git a/libs/vkd3d-shader/dxil.c b/libs/vkd3d-shader/dxil.c
index 7c711d7c..ebd78909 100644
--- a/libs/vkd3d-shader/dxil.c
+++ b/libs/vkd3d-shader/dxil.c
@@ -581,6 +581,7 @@ struct sm6_parser
     size_t descriptor_count;
 
     unsigned int indexable_temp_count;
+    unsigned int icb_count;
 
     struct sm6_value *values;
     size_t value_count;
@@ -2433,6 +2434,7 @@ static enum vkd3d_result value_allocate_constant_array(struct sm6_value *dst, co
     dst->value_type = VALUE_TYPE_ICB;
     dst->u.icb = icb;
 
+    icb->register_idx = sm6->icb_count++;
     icb->data_type = vkd3d_data_type_from_sm6_type(elem_type);
     icb->element_count = type->u.array.count;
     icb->component_count = 1;
diff --git a/libs/vkd3d-shader/spirv.c b/libs/vkd3d-shader/spirv.c
index 633bd7ce..dc3d9631 100644
--- a/libs/vkd3d-shader/spirv.c
+++ b/libs/vkd3d-shader/spirv.c
@@ -2162,6 +2162,7 @@ static void vkd3d_symbol_make_register(struct vkd3d_symbol *symbol,
             break;
 
         case VKD3DSPR_IMMCONSTBUFFER:
+            symbol->key.reg.idx = reg->idx_count > 1 ? reg->idx[0].offset : 0;
             break;
 
         default:
@@ -3508,7 +3509,7 @@ static void spirv_compiler_emit_dereference_register(struct spirv_compiler *comp
     }
     else if (reg->type == VKD3DSPR_IMMCONSTBUFFER)
     {
-        indexes[index_count++] = spirv_compiler_emit_register_addressing(compiler, &reg->idx[0]);
+        indexes[index_count++] = spirv_compiler_emit_register_addressing(compiler, &reg->idx[reg->idx_count - 1]);
     }
     else if (reg->type == VKD3DSPR_IDXTEMP)
     {
@@ -5828,7 +5829,9 @@ static void spirv_compiler_emit_dcl_immediate_constant_buffer(struct spirv_compi
             ptr_type_id, SpvStorageClassPrivate, const_id);
     vkd3d_spirv_build_op_name(builder, icb_id, "icb");
 
-    vsir_register_init(&reg, VKD3DSPR_IMMCONSTBUFFER, VKD3D_DATA_FLOAT, 0);
+    /* Set an index count of 2 so vkd3d_symbol_make_register() uses idx[0] as a buffer id. */
+    vsir_register_init(&reg, VKD3DSPR_IMMCONSTBUFFER, VKD3D_DATA_FLOAT, 2);
+    reg.idx[0].offset = icb->register_idx;
     vkd3d_symbol_make_register(&reg_symbol, &reg);
     vkd3d_symbol_set_register_info(&reg_symbol, icb_id, SpvStorageClassPrivate,
                 vkd3d_component_type_from_data_type(icb->data_type),
diff --git a/libs/vkd3d-shader/tpf.c b/libs/vkd3d-shader/tpf.c
index ba504c41..163cd90e 100644
--- a/libs/vkd3d-shader/tpf.c
+++ b/libs/vkd3d-shader/tpf.c
@@ -792,6 +792,7 @@ static void shader_sm4_read_shader_data(struct vkd3d_shader_instruction *ins, ui
         ins->handler_idx = VKD3DSIH_INVALID;
         return;
     }
+    icb->register_idx = 0;
     icb->data_type = VKD3D_DATA_FLOAT;
     icb->component_count = VKD3D_VEC4_SIZE;
     icb->element_count = icb_size / VKD3D_VEC4_SIZE;
@@ -1931,6 +1932,15 @@ static bool shader_sm4_read_param(struct vkd3d_shader_sm4_parser *priv, const ui
                 break;
         }
     }
+    else if (register_type == VKD3D_SM4_RT_IMMCONSTBUFFER)
+    {
+        if (param->idx_count != 1)
+        {
+            WARN("Unexpected idx count %u.\n", param->idx_count);
+            vkd3d_shader_parser_error(&priv->p, VKD3D_SHADER_ERROR_TPF_INVALID_REGISTER_INDEX_COUNT,
+                    "Invalid index count %u for immediate const buffer register; expected count 1.", param->idx_count);
+        }
+    }
     else if (!shader_is_sm_5_1(priv) && vsir_register_is_descriptor(param))
     {
         /* SM5.1 places a symbol identifier in idx[0] and moves
diff --git a/libs/vkd3d-shader/vkd3d_shader_private.h b/libs/vkd3d-shader/vkd3d_shader_private.h
index 3458b8f5..a94a8152 100644
--- a/libs/vkd3d-shader/vkd3d_shader_private.h
+++ b/libs/vkd3d-shader/vkd3d_shader_private.h
@@ -793,6 +793,7 @@ struct vkd3d_shader_version
 
 struct vkd3d_shader_immediate_constant_buffer
 {
+    unsigned int register_idx;
     enum vkd3d_data_type data_type;
     /* total count is element_count * component_count */
     unsigned int element_count;