diff --git a/src/jrd/Database.cpp b/src/jrd/Database.cpp
index f01dfb7529..8a66048426 100644
--- a/src/jrd/Database.cpp
+++ b/src/jrd/Database.cpp
@@ -231,6 +231,19 @@ namespace Jrd
 		dbb_flags &= ~(DBB_sweep_in_progress | DBB_sweep_starting);
 	}
 
+	void Database::registerModule(Module& module)
+	{
+		Sync sync(&dbb_modules_sync, FB_FUNCTION);
+		sync.lock(SYNC_SHARED);
+		if (dbb_modules.exist(module))
+			return;
+
+		sync.unlock();
+		sync.lock(SYNC_EXCLUSIVE);
+		if (!dbb_modules.exist(module))
+			dbb_modules.add(module);
+	}
+
 	void Database::SharedCounter::shutdown(thread_db* tdbb)
 	{
 		for (size_t i = 0; i < TOTAL_ITEMS; i++)
diff --git a/src/jrd/Database.h b/src/jrd/Database.h
index d15554e727..b8be9f1dba 100644
--- a/src/jrd/Database.h
+++ b/src/jrd/Database.h
@@ -398,7 +398,11 @@ public:
 
 	MonitoringData*			dbb_monitoring_data;	// monitoring data
 
+private:
+	Firebird::SyncObject dbb_modules_sync;
 	DatabaseModules	dbb_modules;		// external function/filter modules
+
+public:
 	ExtEngineManager dbb_extManager;	// external engine manager
 
 	Firebird::SyncObject	dbb_flush_count_mutex;
@@ -497,6 +501,8 @@ public:
 
 	void deletePool(MemoryPool* pool);
 
+	void registerModule(Module&);
+
 private:
 	Database(MemoryPool* p, Firebird::IPluginConfig* pConf, bool shared)
 	:	dbb_permanent(p),
diff --git a/src/jrd/Function.epp b/src/jrd/Function.epp
index 3ca90daa58..357ee9ecf6 100644
--- a/src/jrd/Function.epp
+++ b/src/jrd/Function.epp
@@ -389,7 +389,7 @@ Function* Function::loadMetadata(thread_db* tdbb, USHORT id, bool noscan, USHORT
 			if (!X.RDB$MODULE_NAME.NULL && !X.RDB$ENTRYPOINT.NULL)
 			{
 				function->fun_entrypoint =
-					Module::lookup(X.RDB$MODULE_NAME, X.RDB$ENTRYPOINT, dbb->dbb_modules);
+					Module::lookup(X.RDB$MODULE_NAME, X.RDB$ENTRYPOINT, dbb);
 
 				// Could not find a function with given MODULE, ENTRYPOINT.
 				// Try the list of internally implemented functions.
diff --git a/src/jrd/flu.cpp b/src/jrd/flu.cpp
index 60d5d7e735..9f5ea61ceb 100644
--- a/src/jrd/flu.cpp
+++ b/src/jrd/flu.cpp
@@ -165,7 +165,7 @@ namespace Jrd
 	}
 
 
-	FPTR_INT Module::lookup(const char* module, const char* name, DatabaseModules& interest)
+	FPTR_INT Module::lookup(const char* module, const char* name, Database* dbb)
 	{
 		// Try to find loadable module
 		Module m = lookupModule(module);
@@ -178,12 +178,7 @@ namespace Jrd
 		terminate_at_space(symbol, name);
 		void* rc = m.lookupSymbol(symbol);
 		if (rc)
-		{
-			if (!interest.exist(m))
-			{
-				interest.add(m);
-			}
-		}
+			dbb->registerModule(m);
 
 		return (FPTR_INT)rc;
 	}
diff --git a/src/jrd/flu.h b/src/jrd/flu.h
index 9faabd0926..ff6cd60e8a 100644
--- a/src/jrd/flu.h
+++ b/src/jrd/flu.h
@@ -35,6 +35,8 @@
 
 namespace Jrd
 {
+	class Database;
+
 	class Module
 	{
 	private:
@@ -105,7 +107,7 @@ namespace Jrd
 		~Module();
 
 		// used for UDF/BLOB Filter
-		static FPTR_INT lookup(const char*, const char*, Firebird::SortedObjectsArray<Module>&);
+		static FPTR_INT lookup(const char*, const char*, Database*);
 
 		bool operator>(const Module &im) const;
 
diff --git a/src/jrd/met.epp b/src/jrd/met.epp
index 89927439ff..d2ea63e105 100644
--- a/src/jrd/met.epp
+++ b/src/jrd/met.epp
@@ -2264,7 +2264,7 @@ BlobFilter* MET_lookup_filter(thread_db* tdbb, SSHORT from, SSHORT to)
 		X.RDB$OUTPUT_SUB_TYPE EQ to
 	{
 		filter = (FPTR_BFILTER_CALLBACK)
-			Module::lookup(X.RDB$MODULE_NAME, X.RDB$ENTRYPOINT, dbb->dbb_modules);
+			Module::lookup(X.RDB$MODULE_NAME, X.RDB$ENTRYPOINT, dbb);
 		if (filter)
 		{
 			blf = FB_NEW_POOL(*dbb->dbb_permanent) BlobFilter(*dbb->dbb_permanent);