diff --git a/docs/libcurl/opts/CURLOPT_DNS_INTERFACE.3 b/docs/libcurl/opts/CURLOPT_DNS_INTERFACE.3
index 699ed678c5..90c7030bcb 100644
--- a/docs/libcurl/opts/CURLOPT_DNS_INTERFACE.3
+++ b/docs/libcurl/opts/CURLOPT_DNS_INTERFACE.3
@@ -42,6 +42,7 @@ option.
 .SH DEFAULT
 NULL
 .SH PROTOCOLS
+All protocols except file:// - protocols that resolve host names.
 .SH EXAMPLE
 .nf
 CURL *curl = curl_easy_init();