diff --git a/src/http/modules/ngx_http_grpc_module.c b/src/http/modules/ngx_http_grpc_module.c
index 654bd17..65bd1e6 100644
--- a/src/http/modules/ngx_http_grpc_module.c
+++ b/src/http/modules/ngx_http_grpc_module.c
@@ -3384,7 +3384,7 @@
             return NGX_ERROR;
         }
 
-        if (ch == '\0' || ch == CR || ch == LF) {
+        if (ch <= 0x20 || ch == 0x7f) {
             return NGX_ERROR;
         }
     }
diff --git a/src/http/ngx_http_parse.c b/src/http/ngx_http_parse.c
index 0d36a44..6af326d 100644
--- a/src/http/ngx_http_parse.c
+++ b/src/http/ngx_http_parse.c
@@ -893,7 +893,7 @@
                     break;
                 }
 
-                if (ch == '\0') {
+                if (ch <= 0x20 || ch == 0x7f || ch == ':') {
                     return NGX_HTTP_PARSE_INVALID_HEADER;
                 }
 
@@ -961,7 +961,7 @@
                 break;
             }
 
-            if (ch == '\0') {
+            if (ch <= 0x20 || ch == 0x7f) {
                 return NGX_HTTP_PARSE_INVALID_HEADER;
             }
 
diff --git a/src/http/v2/ngx_http_v2.c b/src/http/v2/ngx_http_v2.c
index 423667d..3bef002 100644
--- a/src/http/v2/ngx_http_v2.c
+++ b/src/http/v2/ngx_http_v2.c
@@ -3457,7 +3457,7 @@
             continue;
         }
 
-        if (ch == '\0' || ch == LF || ch == CR || ch == ':'
+        if (ch <= 0x20 || ch == 0x7f || ch == ':'
             || (ch >= 'A' && ch <= 'Z'))
         {
             ngx_log_error(NGX_LOG_INFO, r->connection->log, 0,