diff --git a/include/NetworkInterface.h b/include/NetworkInterface.h
index 9f69101459..96f776fffb 100644
--- a/include/NetworkInterface.h
+++ b/include/NetworkInterface.h
@@ -668,7 +668,7 @@ class NetworkInterface : public AlertableEntity {
   void reloadHideFromTop(bool refreshHosts=true);
   void updateLbdIdentifier();
   inline bool serializeLbdHostsAsMacs()             { return(lbd_serialize_by_mac); }
-  void startCustomCategoriesReload();
+  bool startCustomCategoriesReload();
   void cleanShadownDPI();
   void checkReloadHostsBroadcastDomain();
   inline bool reloadHostsBroadcastDomain()          { return reload_hosts_bcast_domain; }
diff --git a/include/Ntop.h b/include/Ntop.h
index bea2767ba5..75c6513b93 100644
--- a/include/Ntop.h
+++ b/include/Ntop.h
@@ -430,7 +430,7 @@ class Ntop {
   DeviceProtoStatus getDeviceAllowedProtocolStatus(DeviceType dev_type, ndpi_protocol proto, u_int16_t pool_id, bool as_client);
   void refreshCpuLoad();
   bool getCpuLoad(float *out);
-  inline bool canSafelyReloadnDPI(time_t now)             { return((now - last_ndpi_reload) >= MIN_NDPI_RELOAD_INTERVAL); }
+  bool canSafelyReloadnDPI(time_t now);
   inline void setLastInterfacenDPIReload(time_t now)      { last_ndpi_reload = now;   }
   inline bool needsnDPICleanup(time_t now)                { return(ndpi_cleanup_needed && canSafelyReloadnDPI(now)); }
   inline void setnDPICleanupNeeded(bool needed)           { ndpi_cleanup_needed = needed; }
diff --git a/include/ntop_defines.h b/include/ntop_defines.h
index e1b0a5579d..cb92991b22 100644
--- a/include/ntop_defines.h
+++ b/include/ntop_defines.h
@@ -619,7 +619,7 @@
 #endif
 #define CONST_RUNTIME_PREFS_HOSTMASK  NTOPNG_PREFS_PREFIX".host_mask"
 #define CONST_RUNTIME_PREFS_AUTO_ASSIGNED_POOL_ID      NTOPNG_PREFS_PREFIX".auto_assigned_pool_id"
-#define MIN_NDPI_RELOAD_INTERVAL                       120 /* sec, needed to avoid freeing the shadow pointer too early */
+#define MIN_NDPI_RELOAD_INTERVAL                       10 /* sec, needed to avoid freeing the shadow pointer too early */
 
 #define CONST_MAX_ALERT_MSG_QUEUE_LEN 8192
 #define CONST_MAX_ES_MSG_QUEUE_LEN    8192
diff --git a/src/LuaEngine.cpp b/src/LuaEngine.cpp
index 7a70b3a47d..ff19b11323 100644
--- a/src/LuaEngine.cpp
+++ b/src/LuaEngine.cpp
@@ -1803,13 +1803,16 @@ static int ntop_startCustomCategoriesReload(lua_State* vm) {
     return(CONST_LUA_OK);
   }
 
-  ntop->setLastInterfacenDPIReload(time(NULL));
-  
   for(int i=0; i<ntop->get_num_interfaces(); i++) {
     NetworkInterface *iface;
 
-    if((iface = ntop->getInterface(i)) != NULL)
-      iface->startCustomCategoriesReload();
+    if((iface = ntop->getInterface(i)) != NULL) {
+      if(!iface->startCustomCategoriesReload()) {
+	/* startCustomCategoriesReload, abort */
+	lua_pushboolean(vm, false);
+	return(CONST_LUA_OK);
+      }
+    }
   }
 
   lua_pushboolean(vm, true /* can now start reloading */);
@@ -1899,6 +1902,7 @@ static int ntop_reloadCustomCategories(lua_State* vm) {
   }
 
   ntop->getTrace()->traceEvent(TRACE_DEBUG, "Category lists reload done");
+  ntop->setLastInterfacenDPIReload(time(NULL));
   ntop->setnDPICleanupNeeded(true);
 
   lua_pushboolean(vm, true /* reload performed */);
diff --git a/src/NetworkInterface.cpp b/src/NetworkInterface.cpp
index 2d3ae5674c..8e26c1092f 100644
--- a/src/NetworkInterface.cpp
+++ b/src/NetworkInterface.cpp
@@ -355,7 +355,7 @@ struct ndpi_detection_module_struct* NetworkInterface::initnDPIStruct() {
 void NetworkInterface::cleanShadownDPI() {
   ntop->getTrace()->traceEvent(TRACE_NORMAL, "%s(%p)", __FUNCTION__, ndpi_struct_shadow);
   
-  if(ndpi_struct_shadow) {
+  if(ndpi_struct_shadow && !ndpiReloadInProgress) {
     ndpi_exit_detection_module(ndpi_struct_shadow);
     ndpi_struct_shadow = NULL;
   }
@@ -370,21 +370,22 @@ void NetworkInterface::cleanShadownDPI() {
  * 3. reloadCustomCategories()
  * 4. cleanShadownDPI()
  */
-void NetworkInterface::startCustomCategoriesReload() {
+bool NetworkInterface::startCustomCategoriesReload() {
   ntop->getTrace()->traceEvent(TRACE_NORMAL, "Started nDPI reload on %s [%p][%s]", get_name(), ndpi_struct_shadow, ndpiReloadInProgress ? "IN PROGRESS" : "");
 
   if(ndpiReloadInProgress) {
     ntop->getTrace()->traceEvent(TRACE_ERROR, "Internal error: nested nDPI category reload");
-    return;
-  } else
-    ndpiReloadInProgress = true;
-  
+    return(false);
+  }
+
   cleanShadownDPI();
+  ndpiReloadInProgress = true;
 
   /* No need to dedicate another variable for the reload, we can use the shadow itself */
   ndpi_struct_shadow = initnDPIStruct();
-  ntop->getTrace()->traceEvent(TRACE_NORMAL, "Completed nDPI reload on %s [%p]",
+  ntop->getTrace()->traceEvent(TRACE_NORMAL, "nDPI reload is now ready on %s [%p]",
 			       get_name(), ndpi_struct_shadow);
+  return(true);
 }
 
 /* **************************************************** */
diff --git a/src/Ntop.cpp b/src/Ntop.cpp
index fd5f1fcfef..5a55cf3b7a 100644
--- a/src/Ntop.cpp
+++ b/src/Ntop.cpp
@@ -2317,3 +2317,12 @@ void Ntop::reloadJA3Hashes() {
   malicious_ja3 = new_malicious_ja3;
   new_malicious_ja3 = new std::set<std::string>();
 }
+
+/* ******************************************* */
+
+/* This ensures that a network interface is not still using the old ndpi struct
+ * (stored in ndpi_struct_shadow) while a reload is in progress.
+ */
+bool Ntop::canSafelyReloadnDPI(time_t now) {
+  return((now - last_ndpi_reload) >= MIN_NDPI_RELOAD_INTERVAL);
+}