--- a/src/http/ngx_http_core_module.c
+++ b/src/http/ngx_http_core_module.c
@@ -231,6 +231,13 @@ static ngx_command_t  ngx_http_core_comm
       offsetof(ngx_http_core_srv_conf_t, merge_slashes),
       NULL },
 
+    { ngx_string("underscores_in_headers"),
+      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_CONF_FLAG,
+      ngx_conf_set_flag_slot,
+      NGX_HTTP_SRV_CONF_OFFSET,
+      offsetof(ngx_http_core_srv_conf_t, underscores_in_headers),
+      NULL },
+
     { ngx_string("location"),
       NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_BLOCK|NGX_CONF_TAKE12,
       ngx_http_core_location,
@@ -2527,6 +2534,7 @@ ngx_http_core_create_srv_conf(ngx_conf_t
     cscf->client_header_buffer_size = NGX_CONF_UNSET_SIZE;
     cscf->ignore_invalid_headers = NGX_CONF_UNSET;
     cscf->merge_slashes = NGX_CONF_UNSET;
+    cscf->underscores_in_headers = NGX_CONF_UNSET;
 
     return cscf;
 }
@@ -2605,6 +2613,9 @@ ngx_http_core_merge_srv_conf(ngx_conf_t 
 
     ngx_conf_merge_value(conf->merge_slashes, prev->merge_slashes, 1);
 
+    ngx_conf_merge_value(conf->underscores_in_headers,
+                              prev->underscores_in_headers, 0);
+
     return NGX_CONF_OK;
 }