diff --git a/src/core/ngx_buf.h b/src/core/ngx_buf.h
index 00522cce5..224807cb0 100644
--- a/src/core/ngx_buf.h
+++ b/src/core/ngx_buf.h
@@ -88,9 +88,7 @@ struct ngx_output_chain_ctx_s {
     unsigned                     unaligned:1;
     unsigned                     need_in_memory:1;
     unsigned                     need_in_temp:1;
-#if (NGX_HAVE_FILE_AIO || NGX_THREADS)
     unsigned                     aio:1;
-#endif
 
 #if (NGX_HAVE_FILE_AIO)
     ngx_output_chain_aio_pt      aio_handler;
@@ -99,7 +97,7 @@ struct ngx_output_chain_ctx_s {
 #endif
 #endif
 
-#if (NGX_THREADS)
+#if (NGX_THREADS || NGX_COMPAT)
     ngx_int_t                  (*thread_handler)(ngx_thread_task_t *task,
                                                  ngx_file_t *file);
     ngx_thread_task_t           *thread_task;
diff --git a/src/core/ngx_connection.h b/src/core/ngx_connection.h
index 1472090e5..b527954e6 100644
--- a/src/core/ngx_connection.h
+++ b/src/core/ngx_connection.h
@@ -186,7 +186,7 @@ struct ngx_connection_s {
     unsigned            busy_count:2;
 #endif
 
-#if (NGX_THREADS)
+#if (NGX_THREADS || NGX_COMPAT)
     ngx_thread_task_t  *sendfile_task;
 #endif
 };
diff --git a/src/core/ngx_core.h b/src/core/ngx_core.h
index 2819c1a7d..8f8489fcb 100644
--- a/src/core/ngx_core.h
+++ b/src/core/ngx_core.h
@@ -12,22 +12,19 @@
 #include <ngx_config.h>
 
 
-typedef struct ngx_module_s      ngx_module_t;
-typedef struct ngx_conf_s        ngx_conf_t;
-typedef struct ngx_cycle_s       ngx_cycle_t;
-typedef struct ngx_pool_s        ngx_pool_t;
-typedef struct ngx_chain_s       ngx_chain_t;
-typedef struct ngx_log_s         ngx_log_t;
-typedef struct ngx_open_file_s   ngx_open_file_t;
-typedef struct ngx_command_s     ngx_command_t;
-typedef struct ngx_file_s        ngx_file_t;
-typedef struct ngx_event_s       ngx_event_t;
-typedef struct ngx_event_aio_s   ngx_event_aio_t;
-typedef struct ngx_connection_s  ngx_connection_t;
-
-#if (NGX_THREADS)
+typedef struct ngx_module_s       ngx_module_t;
+typedef struct ngx_conf_s         ngx_conf_t;
+typedef struct ngx_cycle_s        ngx_cycle_t;
+typedef struct ngx_pool_s         ngx_pool_t;
+typedef struct ngx_chain_s        ngx_chain_t;
+typedef struct ngx_log_s          ngx_log_t;
+typedef struct ngx_open_file_s    ngx_open_file_t;
+typedef struct ngx_command_s      ngx_command_t;
+typedef struct ngx_file_s         ngx_file_t;
+typedef struct ngx_event_s        ngx_event_t;
+typedef struct ngx_event_aio_s    ngx_event_aio_t;
+typedef struct ngx_connection_s   ngx_connection_t;
 typedef struct ngx_thread_task_s  ngx_thread_task_t;
-#endif
 
 typedef void (*ngx_event_handler_pt)(ngx_event_t *ev);
 typedef void (*ngx_connection_handler_pt)(ngx_connection_t *c);
diff --git a/src/core/ngx_file.h b/src/core/ngx_file.h
index 5c4482193..cff74cba1 100644
--- a/src/core/ngx_file.h
+++ b/src/core/ngx_file.h
@@ -23,7 +23,7 @@ struct ngx_file_s {
 
     ngx_log_t                 *log;
 
-#if (NGX_THREADS)
+#if (NGX_THREADS || NGX_COMPAT)
     ngx_int_t                (*thread_handler)(ngx_thread_task_t *task,
                                                ngx_file_t *file);
     void                      *thread_ctx;
diff --git a/src/core/ngx_module.h b/src/core/ngx_module.h
index 10a7eabaf..626481d8a 100644
--- a/src/core/ngx_module.h
+++ b/src/core/ngx_module.h
@@ -127,7 +127,7 @@
 #define NGX_MODULE_SIGNATURE_21  "0"
 #endif
 
-#if (NGX_THREADS)
+#if (NGX_THREADS || NGX_COMPAT)
 #define NGX_MODULE_SIGNATURE_22  "1"
 #else
 #define NGX_MODULE_SIGNATURE_22  "0"
diff --git a/src/event/ngx_event_pipe.h b/src/event/ngx_event_pipe.h
index ef2e7a006..10a334027 100644
--- a/src/event/ngx_event_pipe.h
+++ b/src/event/ngx_event_pipe.h
@@ -47,7 +47,7 @@ struct ngx_event_pipe_s {
     ngx_event_pipe_output_filter_pt   output_filter;
     void                             *output_ctx;
 
-#if (NGX_THREADS)
+#if (NGX_THREADS || NGX_COMPAT)
     ngx_int_t                       (*thread_handler)(ngx_thread_task_t *task,
                                                       ngx_file_t *file);
     void                             *thread_ctx;
diff --git a/src/http/ngx_http_cache.h b/src/http/ngx_http_cache.h
index 9c9ff6f65..70342d0ed 100644
--- a/src/http/ngx_http_cache.h
+++ b/src/http/ngx_http_cache.h
@@ -93,7 +93,7 @@ struct ngx_http_cache_s {
     ngx_http_file_cache_t           *file_cache;
     ngx_http_file_cache_node_t      *node;
 
-#if (NGX_THREADS)
+#if (NGX_THREADS || NGX_COMPAT)
     ngx_thread_task_t               *thread_task;
 #endif
 
diff --git a/src/http/ngx_http_core_module.h b/src/http/ngx_http_core_module.h
index 628679ff3..7140a6b7a 100644
--- a/src/http/ngx_http_core_module.h
+++ b/src/http/ngx_http_core_module.h
@@ -15,6 +15,8 @@
 
 #if (NGX_THREADS)
 #include <ngx_thread_pool.h>
+#elif (NGX_COMPAT)
+typedef struct ngx_thread_pool_s  ngx_thread_pool_t;
 #endif
 
 
@@ -409,7 +411,7 @@ struct ngx_http_core_loc_conf_s {
 #endif
 #endif
 
-#if (NGX_THREADS)
+#if (NGX_THREADS || NGX_COMPAT)
     ngx_thread_pool_t         *thread_pool;
     ngx_http_complex_value_t  *thread_pool_value;
 #endif