diff --git a/include/libssh/dh.h b/include/libssh/dh.h
index f28b9169..89872e30 100644
--- a/include/libssh/dh.h
+++ b/include/libssh/dh.h
@@ -49,7 +49,9 @@ int hashbufin_add_cookie(ssh_session session, unsigned char *cookie);
 int hashbufout_add_cookie(ssh_session session);
 int generate_session_keys(ssh_session session);
 bignum make_string_bn(ssh_string string);
+#ifdef HAVE_LIBCRYPTO
 void make_string_bn_inplace(ssh_string string, bignum bnout);
+#endif /* HAVE_LIBCRYPTO */
 ssh_string make_bignum_string(bignum num);
 
 #endif /* DH_H_ */
diff --git a/src/dh.c b/src/dh.c
index 84355d48..010a1dda 100644
--- a/src/dh.c
+++ b/src/dh.c
@@ -407,14 +407,17 @@ bignum make_string_bn(ssh_string string){
   return bn;
 }
 
+#ifdef HAVE_LIBCRYPTO
+/** @internal
+ * @brief converts the content of a SSH string in an already allocated bignum
+ * @warning only available with OpenSSL builds
+ */
 void make_string_bn_inplace(ssh_string string, bignum bnout) {
   unsigned int len = ssh_string_len(string);
-#ifdef HAVE_LIBGCRYPT
-  #error "unsupported"
-#elif defined HAVE_LIBCRYPTO
   bignum_bin2bn(string->data, len, bnout);
-#endif
 }
+#endif /* HAVE_LIBCRYPTO */
+
 
 ssh_string dh_get_e(ssh_session session) {
   return make_bignum_string(session->next_crypto->e);