diff --git a/lib/url.c b/lib/url.c
index 19388437a..6795a9c8f 100644
--- a/lib/url.c
+++ b/lib/url.c
@@ -6984,7 +6984,7 @@ CURLcode Curl_init_do(struct Curl_easy *data, struct connectdata *conn)
 * Returns the family as a single bit protocol identifier.
 */
 
-unsigned int get_protocol_family(unsigned int protocol)
+static unsigned int get_protocol_family(unsigned int protocol)
 {
   unsigned int family;