diff --git a/src/common/classes/Synchronize.cpp b/src/common/classes/Synchronize.cpp
index 7a09ec89fb..51f3222df4 100644
--- a/src/common/classes/Synchronize.cpp
+++ b/src/common/classes/Synchronize.cpp
@@ -31,6 +31,7 @@
 
 #include "firebird.h"
 #include "fb_tls.h"
+#include "init.h"
 #include "../ThreadStart.h"
 #include "SyncObject.h"
 #include "Synchronize.h"
@@ -182,6 +183,37 @@ void Synchronize::shutdown()
 }
 
 
+class ThreadSyncInstance : public ThreadSync
+{
+	typedef InstanceControl::InstanceLink<ThreadSyncInstance, InstanceControl::PRIORITY_REGULAR> Link;
+
+public:
+	ThreadSyncInstance(const char* desc)
+		: ThreadSync(desc)
+	{
+		m_link = FB_NEW Link(this);
+	}
+
+	virtual ~ThreadSyncInstance()
+	{
+		if (m_link)
+		{
+			m_link->remove();
+			delete m_link;
+		}
+	}
+
+	// Used at InstanceControl::dtor
+	void dtor()
+	{
+		m_link = nullptr;
+		delete this;
+	}
+
+private:
+	Link* m_link;
+};
+
 /// ThreadSync
 
 TLS_DECLARE(ThreadSync*, threadIndex);
@@ -210,7 +242,7 @@ ThreadSync* ThreadSync::getThread(const char* desc)
 
 	if (!thread)
 	{
-		thread = FB_NEW ThreadSync(desc);
+		thread = FB_NEW ThreadSyncInstance(desc);
 
 		fb_assert(thread == findThread());
 	}
@@ -220,6 +252,12 @@ ThreadSync* ThreadSync::getThread(const char* desc)
 
 void ThreadSync::setThread(ThreadSync* thread)
 {
+	if (thread != NULL)
+	{
+		ThreadSync* other = findThread();
+		fb_assert(other == NULL);
+	}
+
 	TLS_SET(threadIndex, thread);
 }
 
diff --git a/src/common/classes/init.cpp b/src/common/classes/init.cpp
index 9f28f6e720..c477f3eb6a 100644
--- a/src/common/classes/init.cpp
+++ b/src/common/classes/init.cpp
@@ -227,12 +227,37 @@ namespace Firebird
 	{
 		MutexLockGuard guard(*StaticMutex::mutex, "InstanceControl::InstanceList::InstanceList");
 		next = instanceList;
+		prev = nullptr;
+		if (instanceList)
+			instanceList->prev = this;
 		instanceList = this;
 	}
 
 	InstanceControl::InstanceList::~InstanceList()
 	{
-		delete next;
+		fb_assert(next == nullptr);
+		fb_assert(prev == nullptr);
+	}
+
+	void InstanceControl::InstanceList::remove()
+	{
+		MutexLockGuard guard(*StaticMutex::mutex, FB_FUNCTION);
+		unlist();
+	}
+
+	void InstanceControl::InstanceList::unlist()
+	{
+		if (instanceList == this)
+			instanceList = next;
+
+		if (next)
+			next->prev = this->prev;
+
+		if (prev)
+			prev->next = this->next;
+
+		prev = nullptr;
+		next = nullptr;
 	}
 
 	void InstanceControl::destructors()
@@ -299,8 +324,13 @@ namespace Firebird
 			}
 		} while (nextPriority != currentPriority);
 
-		delete instanceList;
-		instanceList = 0;
+
+		while (instanceList)
+		{
+			InstanceList* item = instanceList;
+			item->unlist();
+			delete item;
+		}
 	}
 
 	void InstanceControl::registerGdsCleanup(FPTR_VOID cleanup)
diff --git a/src/common/classes/init.h b/src/common/classes/init.h
index 3ce0e06cdf..5787828733 100644
--- a/src/common/classes/init.h
+++ b/src/common/classes/init.h
@@ -71,10 +71,16 @@ public:
 		virtual ~InstanceList();
 		static void destructors();
 
+		// remove self from common list under StaticMutex protection
+		void remove();
+
 	private:
-		InstanceList* next;
-		DtorPriority priority;
 		virtual void dtor() = 0;
+		void unlist();
+
+		InstanceList* next;
+		InstanceList* prev;
+		DtorPriority priority;
 	};
 
 	template <typename T, InstanceControl::DtorPriority P = InstanceControl::PRIORITY_REGULAR>
@@ -90,6 +96,11 @@ public:
 			fb_assert(link);
 		}
 
+		void remove()
+		{
+			InstanceList::remove();
+		}
+
 		void dtor()
 		{
 			fb_assert(link);