diff --git a/src/jrd/Attachment.h b/src/jrd/Attachment.h
index fd5873d43b..5b89720b9f 100644
--- a/src/jrd/Attachment.h
+++ b/src/jrd/Attachment.h
@@ -385,11 +385,7 @@ public:
 
 	JAttachment* getInterface() throw();
 
-	JProvider* getProvider()
-	{
-		fb_assert(att_provider);
-		return att_provider;
-	}
+	JProvider* getProvider();
 
 private:
 	Attachment(MemoryPool* pool, Database* dbb, JProvider* provider);
@@ -461,6 +457,12 @@ inline bool Attachment::isUtility() const
 	return (att_utility != UTIL_NONE);
 }
 
+inline JProvider* Attachment::getProvider()
+{
+	fb_assert(att_provider || (att_flags & ATT_system));
+	return att_provider;
+}
+
 // This class holds references to all attachments it contains
 
 class AttachmentsRefHolder
diff --git a/src/jrd/ExtEngineManager.cpp b/src/jrd/ExtEngineManager.cpp
index 468485d1e5..778bdb7ac2 100644
--- a/src/jrd/ExtEngineManager.cpp
+++ b/src/jrd/ExtEngineManager.cpp
@@ -603,8 +603,13 @@ ExtEngineManager::ExternalContextImpl::ExternalContextImpl(thread_db* tdbb,
 
 	internalAttachment->getStable()->addRef();
 
-	externalAttachment = MasterInterfacePtr()->registerAttachment
-		(internalAttachment->getProvider(), internalAttachment->getInterface());
+	Jrd::JProvider* jProv = internalAttachment->getProvider();
+	Jrd::JAttachment* jAtt = internalAttachment->getInterface();
+
+	// System attachments (such as garbage collector) have no external interface
+	// and should not be used by UDR's
+	if (jProv && jAtt)
+		externalAttachment = MasterInterfacePtr()->registerAttachment(jProv, jAtt);
 }
 
 ExtEngineManager::ExternalContextImpl::~ExternalContextImpl()
@@ -616,6 +621,8 @@ ExtEngineManager::ExternalContextImpl::~ExternalContextImpl()
 		externalAttachment->release();
 		externalAttachment = NULL;
 	}
+	else
+		internalAttachment->getStable()->release();
 }
 
 void ExtEngineManager::ExternalContextImpl::releaseTransaction()
@@ -640,7 +647,10 @@ void ExtEngineManager::ExternalContextImpl::setTransaction(thread_db* tdbb)
 	fb_assert(!externalTransaction && !internalTransaction);
 
 	if ((internalTransaction = newTransaction))
-		externalTransaction = MasterInterfacePtr()->registerTransaction(externalAttachment, internalTransaction);
+	{
+		if (externalAttachment)
+			externalTransaction = MasterInterfacePtr()->registerTransaction(externalAttachment, internalTransaction);
+	}
 }
 
 IMaster* ExtEngineManager::ExternalContextImpl::getMaster()
@@ -657,6 +667,8 @@ IExternalEngine* ExtEngineManager::ExternalContextImpl::getEngine(CheckStatusWra
 Firebird::IAttachment* ExtEngineManager::ExternalContextImpl::getAttachment(
 	CheckStatusWrapper* /*status*/)
 {
+	checkExternalAttachment();
+
 	externalAttachment->addRef();
 	return externalAttachment;
 }
@@ -664,6 +676,8 @@ Firebird::IAttachment* ExtEngineManager::ExternalContextImpl::getAttachment(
 Firebird::ITransaction* ExtEngineManager::ExternalContextImpl::getTransaction(
 	CheckStatusWrapper* /*status*/)
 {
+	checkExternalAttachment();
+
 	externalTransaction->addRef();
 	return externalTransaction;
 }
@@ -703,6 +717,13 @@ void* ExtEngineManager::ExternalContextImpl::setInfo(int code, void* value)
 	return oldValue;
 }
 
+void ExtEngineManager::ExternalContextImpl::checkExternalAttachment()
+{
+	if (!externalAttachment)
+	{
+		(Arg::Gds(isc_random) << Arg::Str("Use of system attachment in UDR is not allowed")).raise();
+	}
+}
 
 //---------------------
 
diff --git a/src/jrd/ExtEngineManager.h b/src/jrd/ExtEngineManager.h
index 683fd60ea9..c84494c89b 100644
--- a/src/jrd/ExtEngineManager.h
+++ b/src/jrd/ExtEngineManager.h
@@ -167,6 +167,8 @@ private:
 		void* setInfo(int code, void* value);
 
 	private:
+		void checkExternalAttachment();
+
 		Firebird::IExternalEngine* engine;
 		Attachment* internalAttachment;
 		Firebird::ITransaction* internalTransaction;
diff --git a/src/jrd/vio.cpp b/src/jrd/vio.cpp
index a6b82a140f..363fc52e04 100644
--- a/src/jrd/vio.cpp
+++ b/src/jrd/vio.cpp
@@ -5091,6 +5091,7 @@ void Database::garbage_collector(Database* dbb)
 			TRA_commit(tdbb, transaction, false);
 
 		Monitoring::cleanupAttachment(tdbb);
+		dbb->dbb_extManager.closeAttachment(tdbb, attachment);
 		attachment->releaseLocks(tdbb);
 		LCK_fini(tdbb, LCK_OWNER_attachment);