diff --git a/src/http/ngx_http_parse.c b/src/http/ngx_http_parse.c
index 9777ebb..2fce7ac 100644
--- a/src/http/ngx_http_parse.c
+++ b/src/http/ngx_http_parse.c
@@ -720,7 +720,7 @@
     static u_char  lowcase[] =
         "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
         "\0\0\0\0\0\0\0\0\0\0\0\0\0-\0\0" "0123456789\0\0\0\0\0\0"
-        "\0abcdefghijklmnopqrstuvwxyz\0\0\0\0\0"
+        "\0abcdefghijklmnopqrstuvwxyz\0\0\0\0_"
         "\0abcdefghijklmnopqrstuvwxyz\0\0\0\0\0"
         "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
         "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"