diff --git a/src/common/IntlParametersBlock.h b/src/common/IntlParametersBlock.h
index bc080496dc2..59964ed5dd0 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) = 0;
 	virtual UCHAR getUtf8Tag() = 0;
 
+	virtual ~IntlParametersBlock() = default;
+
 	void toUtf8(ClumpletWriter& pb);
 	void fromUtf8(ClumpletWriter& pb);
 
@@ -74,7 +76,6 @@ class IntlSpbStart : public IntlParametersBlock
 
 	TagType checkTag(UCHAR tag, const char** tagName);
 	UCHAR getUtf8Tag();
-
 private:
 	UCHAR mode;
 };
diff --git a/src/common/ThreadStart.cpp b/src/common/ThreadStart.cpp
index 8496ff22595..0760ad19acc 100644
--- a/src/common/ThreadStart.cpp
+++ b/src/common/ThreadStart.cpp
@@ -181,7 +181,7 @@ Thread Thread::start(ThreadEntryPoint* routine, void* arg, int priority_arg, Han
 	{
 #ifdef HAVE_PTHREAD_CANCEL
 		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);
 #endif
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 fe7b3cc9d36..dda4a998362 100644
--- a/src/common/classes/Hash.h
+++ b/src/common/classes/Hash.h
@@ -103,6 +103,7 @@ namespace Firebird
 
 			void link(Entry** where)
 			{
+				fb_assert(where != nullptr);
 				unLink();
 
 				// set our pointers
diff --git a/src/yvalve/gds.cpp b/src/yvalve/gds.cpp
index fdfe5099fb5..99108e64998 100644
--- a/src/yvalve/gds.cpp
+++ b/src/yvalve/gds.cpp
@@ -2657,7 +2657,7 @@ void API_ROUTINE gds__unregister_cleanup(FPTR_VOID_PTR routine, void *arg)
 	Firebird::MutexLockGuard guard(cleanup_handlers_mutex, "gds__unregister_cleanup");
 
 	clean_t* clean;
-	for (clean_t** clean_ptr = &cleanup_handlers; clean = *clean_ptr; clean_ptr = &clean->clean_next)
+	for (clean_t** clean_ptr = &cleanup_handlers; (clean = *clean_ptr); clean_ptr = &clean->clean_next)
 	{
         if (clean->clean_routine == routine && clean->clean_arg == arg)
 		{