diff --git a/src/http/ngx_http_parse.c b/src/http/ngx_http_parse.c
index 286bec23a..e5dd40e59 100644
--- a/src/http/ngx_http_parse.c
+++ b/src/http/ngx_http_parse.c
@@ -811,6 +811,29 @@ done:
     return NGX_OK;
 }
 
+static ngx_int_t
+ngx_http_non_alnum_dash_header_char(u_char ch)
+{
+    switch (ch) {
+    case '!':
+    case '#':
+    case '$':
+    case '%':
+    case '&':
+    case '\'':
+    case '*':
+    case '+':
+    case '.':
+    case '^':
+    case '_':
+    case '`':
+    case '|':
+    case '~':
+        return 1;
+    default:
+        return 0;
+    }
+}
 
 ngx_int_t
 ngx_http_parse_header_line(ngx_http_request_t *r, ngx_buf_t *b,
@@ -824,7 +847,6 @@ ngx_http_parse_header_line(ngx_http_request_t *r, ngx_buf_t *b,
         sw_space_before_value,
         sw_value,
         sw_space_after_value,
-        sw_ignore_line,
         sw_almost_done,
         sw_header_almost_done
     } state;
@@ -875,22 +897,14 @@ ngx_http_parse_header_line(ngx_http_request_t *r, ngx_buf_t *b,
                     break;
                 }
 
-                if (ch == '_') {
-                    if (allow_underscores) {
-                        hash = ngx_hash(0, ch);
-                        r->lowcase_header[0] = ch;
-                        i = 1;
-
-                    } else {
-                        hash = 0;
-                        i = 0;
-                        r->invalid_header = 1;
-                    }
-
+                if (ch == '_' && allow_underscores) {
+                    hash = ngx_hash(0, ch);
+                    r->lowcase_header[0] = ch;
+                    i = 1;
                     break;
                 }
 
-                if (ch <= 0x20 || ch == 0x7f || ch == ':') {
+                if (!ngx_http_non_alnum_dash_header_char(ch)) {
                     r->header_end = p;
                     return NGX_HTTP_PARSE_INVALID_HEADER;
                 }
@@ -949,17 +963,7 @@ ngx_http_parse_header_line(ngx_http_request_t *r, ngx_buf_t *b,
                 goto done;
             }
 
-            /* IIS may send the duplicate "HTTP/1.1 ..." lines */
-            if (ch == '/'
-                && r->upstream
-                && p - r->header_name_start == 4
-                && ngx_strncmp(r->header_name_start, "HTTP", 4) == 0)
-            {
-                state = sw_ignore_line;
-                break;
-            }
-
-            if (ch <= 0x20 || ch == 0x7f) {
+            if (!ngx_http_non_alnum_dash_header_char(ch)) {
                 r->header_end = p;
                 return NGX_HTTP_PARSE_INVALID_HEADER;
             }
@@ -1034,17 +1038,6 @@ ngx_http_parse_header_line(ngx_http_request_t *r, ngx_buf_t *b,
             }
             break;
 
-        /* ignore header line */
-        case sw_ignore_line:
-            switch (ch) {
-            case LF:
-                state = sw_start;
-                break;
-            default:
-                break;
-            }
-            break;
-
         /* end of header line */
         case sw_almost_done:
             switch (ch) {
@@ -1125,8 +1118,7 @@ ngx_http_v23_validate_header(ngx_http_request_t *r, ngx_str_t *name,
             continue;
         }
 
-        if (ch <= 0x20 || ch == 0x7f || ch == ':'
-            || (ch >= 'A' && ch <= 'Z'))
+        if (!ngx_http_non_alnum_dash_header_char(ch))
         {
             ngx_log_error(NGX_LOG_INFO, r->connection->log, 0,
                           "client sent invalid header name");