--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -2608,6 +2608,21 @@ ngx_http_upstream_response_time_variable
 }
 
 
+ngx_int_t
+ngx_http_upstream_header_variable(ngx_http_request_t *r,
+    ngx_http_variable_value_t *v, uintptr_t data)
+{
+    if (r->upstream == NULL) {
+        v->not_found = 1;
+        return NGX_OK;
+    }
+
+    return ngx_http_variable_unknown_header(v, (ngx_str_t *) data,
+                                         &r->upstream->headers_in.headers.part,
+                                         sizeof("upstream_http_") - 1);
+}
+
+
 static char *
 ngx_http_upstream(ngx_conf_t *cf, ngx_command_t *cmd, void *dummy)
 {