diff --git a/libcli/security/dom_sid.c b/libcli/security/dom_sid.c
index 97f719f3082..2a0b60c3dd7 100644
--- a/libcli/security/dom_sid.c
+++ b/libcli/security/dom_sid.c
@@ -429,7 +429,7 @@ bool dom_sid_is_valid_account_domain(const struct dom_sid *sid)
   string length. If it overflows, return the string length that would
   result (buflen needs to be +1 for the terminating 0).
 */
-int dom_sid_string_buf(const struct dom_sid *sid, char *buf, int buflen)
+static int dom_sid_string_buf(const struct dom_sid *sid, char *buf, int buflen)
 {
 	int i, ofs, ret;
 	uint64_t ia;
diff --git a/libcli/security/dom_sid.h b/libcli/security/dom_sid.h
index d132628da9f..1effdbc2f6c 100644
--- a/libcli/security/dom_sid.h
+++ b/libcli/security/dom_sid.h
@@ -99,7 +99,6 @@ bool dom_sid_in_domain(const struct dom_sid *domain_sid,
 bool dom_sid_is_valid_account_domain(const struct dom_sid *sid);
 
 #define DOM_SID_STR_BUFLEN (15*11+25)
-int dom_sid_string_buf(const struct dom_sid *sid, char *buf, int buflen);
 char *dom_sid_string(TALLOC_CTX *mem_ctx, const struct dom_sid *sid);
 
 struct dom_sid_buf { char buf[DOM_SID_STR_BUFLEN]; };