diff --git a/lib/vtls/x509asn1.c b/lib/vtls/x509asn1.c
index 4c3e7f9f52..3000eb04ff 100644
--- a/lib/vtls/x509asn1.c
+++ b/lib/vtls/x509asn1.c
@@ -427,7 +427,6 @@ static CURLcode utf8asn1str(struct dynbuf *to, int type, const char *from,
  *
  * @unittest 1666
  */
-UNITTEST CURLcode encodeOID(struct dynbuf *buf, const char *b, const char *e);
 UNITTEST CURLcode encodeOID(struct dynbuf *store,
                             const char *beg, const char *end)
 {
diff --git a/lib/vtls/x509asn1.h b/lib/vtls/x509asn1.h
index 829dfd884f..f26297b664 100644
--- a/lib/vtls/x509asn1.h
+++ b/lib/vtls/x509asn1.h
@@ -77,6 +77,9 @@ CURLcode Curl_verifyhost(struct Curl_cfilter *cf, struct Curl_easy *data,
                          const char *beg, const char *end);
 
 #ifdef UNITTESTS
+UNITTEST CURLcode encodeOID(struct dynbuf *store,
+                            const char *beg, const char *end);
+
 #if defined(USE_GNUTLS) || defined(USE_SCHANNEL) || defined(USE_MBEDTLS) || \
   defined(USE_RUSTLS)