diff --git a/src/common/IntlParametersBlock.h b/src/common/IntlParametersBlock.h
index c4bcf73e8d3..b58fd74bb58 100644
--- a/src/common/IntlParametersBlock.h
+++ b/src/common/IntlParametersBlock.h
@@ -44,6 +44,8 @@ class IntlParametersBlock
 	virtual TagType checkTag(UCHAR tag, const char** tagName) noexcept = 0;
 	virtual UCHAR getUtf8Tag() noexcept = 0;
 
+	virtual ~IntlParametersBlock() = default;
+
 	void toUtf8(ClumpletWriter& pb);
 	void fromUtf8(ClumpletWriter& pb);
 
diff --git a/src/common/ThreadStart.cpp b/src/common/ThreadStart.cpp
index b5d6eb12e47..21b658cd9dd 100644
--- a/src/common/ThreadStart.cpp
+++ b/src/common/ThreadStart.cpp
@@ -182,7 +182,7 @@ void Thread::start(ThreadEntryPoint* routine, void* arg, int priority_arg, Threa
 	if (pThread != &thread)
 	{
 		int dummy;		// We do not want to know old cancel type
-		state = pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, &dummy);
+		state = pthread_setcanceltype(PTHREAD_CANCEL_DEFERRED, &dummy);
 		if (state)
 			 Firebird::system_call_failed::raise("pthread_setcanceltype", state);
 	}
diff --git a/src/common/classes/BatchCompletionState.h b/src/common/classes/BatchCompletionState.h
index c8de5d5c0e4..391867c4da4 100644
--- a/src/common/classes/BatchCompletionState.h
+++ b/src/common/classes/BatchCompletionState.h
@@ -34,6 +34,7 @@ namespace Firebird {
 	{
 	public:
 		virtual void transliterate(IStatus* status) = 0;
+		virtual ~Transliterate() = default;
 	};
 
 	class BatchCompletionState final :
diff --git a/src/common/classes/Hash.h b/src/common/classes/Hash.h
index f5dfc8b2e9a..538310c1d1c 100644
--- a/src/common/classes/Hash.h
+++ b/src/common/classes/Hash.h
@@ -103,6 +103,7 @@ namespace Firebird
 
 			void link(Entry** where) noexcept
 			{
+				fb_assert(where != nullptr);
 				unLink();
 
 				// set our pointers