diff --git a/src/AutoConnectCredential.cpp b/src/AutoConnectCredential.cpp
index d7202fe..dd47af1 100644
--- a/src/AutoConnectCredential.cpp
+++ b/src/AutoConnectCredential.cpp
@@ -2,8 +2,8 @@
  *	AutoConnectCredential class dispatcher.
  *	@file	AutoConnectCredential.cpp
  *	@author	hieromon@gmail.com
- *	@version	1.0.0
- *	@date	2019-08-15
+ *	@version	1.0.2
+ *	@date	2019-09-16
  *	@copyright	MIT license.
  */
 
@@ -520,7 +520,7 @@ bool AutoConnectCredential::_del(const char* ssid, const bool commit) {
 uint8_t AutoConnectCredential::_import(void) {
   uint8_t cn = 0;
   if (_pref->begin(AC_CREDENTIAL_NVSNAME, true)) {
-    size_t  psz = _pref->getBytesLength(AC_CREDENTIAL_NVSKEY);
+    size_t  psz = AutoConnectUtil::getPrefBytesLength<Preferences>(_pref.get(), AC_CREDENTIAL_NVSKEY);
     if (psz) {
       uint8_t* credtPool = (uint8_t*)malloc(psz);
       if (credtPool) {
diff --git a/src/AutoConnectCredential.h b/src/AutoConnectCredential.h
index 306a4dc..545145c 100644
--- a/src/AutoConnectCredential.h
+++ b/src/AutoConnectCredential.h
@@ -2,8 +2,8 @@
  *  Declaration of AutoConnectCredential class.
  *  @file AutoConnectCredential.h
  *  @author hieromon@gmail.com
- *  @version  1.0.0
- *  @date 2019-08-15
+ *  @version  1.0.2
+ *  @date 2019-09-16
  *  @copyright  MIT license.
  */
 
@@ -40,6 +40,7 @@ uint8_t  bssid[6];
 wifi_fast_scan_threshold_t threshold;
 };
 #endif
+#include "AutoConnectDefs.h"
 
 /**
  * Credential storage area offset specifier in EEPROM.
@@ -105,12 +106,38 @@ class AutoConnectCredential : public AutoConnectCredentialBase {
 
 #else
 // #pragma message "AutoConnectCredential applies the Preferences"
+#include <type_traits>
 #include <map>
 #include <Preferences.h>
+#include <nvs.h>
 
 #define AC_CREDENTIAL_NVSNAME  AC_IDENTIFIER
 #define AC_CREDENTIAL_NVSKEY   AC_CREDENTIAL_NVSNAME
 
+namespace AutoConnectUtil {
+AC_HAS_FUNC(getBytesLength);
+
+template<typename T>
+typename std::enable_if<AutoConnectUtil::has_func_getBytesLength<T>::value, size_t>::type getPrefBytesLength(T* pref, const char* key) {
+  return pref->getBytesLength(key);
+}
+
+template<typename T>
+typename std::enable_if<!AutoConnectUtil::has_func_getBytesLength<T>::value, size_t>::type getPrefBytesLength(T* pref, const char* key) {
+  AC_UNUSED(pref);
+  uint32_t  handle;
+  size_t    len;
+  esp_err_t err = nvs_open(AC_CREDENTIAL_NVSNAME, NVS_READONLY, &handle);
+  if (err)
+    len = 0;
+  else {
+    (void)nvs_get_blob(handle, key, NULL, &len);
+    nvs_close(handle);
+  }
+  return len;
+}
+}
+
 /** AutoConnectCredential class using Preferences for ESP32 */
 class AutoConnectCredential : public AutoConnectCredentialBase {
  public: