diff --git a/src/Prefs.cpp b/src/Prefs.cpp
index 5f4503627e21..bd00bfa7cd4f 100644
--- a/src/Prefs.cpp
+++ b/src/Prefs.cpp
@@ -219,8 +219,8 @@ Prefs::Prefs(Ntop *_ntop) {
   ls_proto = NULL;
   has_cmdl_trace_lvl = false;
 
-  dns_servers = new (std::nothrow) ServerConfiguration();
-  ntp_servers = new (std::nothrow) ServerConfiguration();
+  dns_servers  = new (std::nothrow) ServerConfiguration();
+  ntp_servers  = new (std::nothrow) ServerConfiguration();
   dhcp_servers = new (std::nothrow) ServerConfiguration();
   smtp_servers = new (std::nothrow) ServerConfiguration();
 
@@ -316,6 +316,11 @@ Prefs::~Prefs() {
   if(modbus_allowed_function_codes)
     ndpi_bitmap_free(modbus_allowed_function_codes);
 #endif
+
+  if(dns_servers)  delete dns_servers;
+  if(ntp_servers)  delete ntp_servers;
+  if(dhcp_servers) delete dhcp_servers;
+  if(smtp_servers) delete smtp_servers;
 }
 
 /* ******************************************* */
@@ -3198,4 +3203,4 @@ bool Prefs::isDHCPServer(IpAddress *ip, u_int16_t vlan_id) {
 
 bool Prefs::isSMTPServer(IpAddress *ip, u_int16_t vlan_id) {
   return smtp_servers->findAddress(ip, vlan_id);
-}
\ No newline at end of file
+}