diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
index c84defaa9..918323d9b 100644
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -5652,7 +5652,7 @@ ngx_http_upstream_copy_content_type(ngx_http_request_t *r, ngx_table_elt_t *h,
 
         last = h->value.data + h->value.len;
 
-        if (*(last - 1) == '"') {
+        if (last > p && *(last - 1) == '"') {
             last--;
         }