diff --git a/src/d_main.cpp b/src/d_main.cpp
index c7a001dfe..02cbca73a 100644
--- a/src/d_main.cpp
+++ b/src/d_main.cpp
@@ -2708,6 +2708,7 @@ void D_DoomMain (void)
 		// clean up game state
 		ST_Clear();
 		D_ErrorCleanup ();
+		DThinker::DestroyThinkersInList(STAT_STATIC);
 		P_FreeLevelData();
 		P_FreeExtraLevelData();
 
diff --git a/src/dthinker.cpp b/src/dthinker.cpp
index da68d8388..fddc28317 100644
--- a/src/dthinker.cpp
+++ b/src/dthinker.cpp
@@ -422,7 +422,7 @@ void DThinker::DestroyAllThinkers ()
 
 	for (i = 0; i <= MAX_STATNUM; i++)
 	{
-		if (i != STAT_TRAVELLING)
+		if (i != STAT_TRAVELLING && i != STAT_STATIC)
 		{
 			DestroyThinkersInList (Thinkers[i]);
 			DestroyThinkersInList (FreshThinkers[i]);
diff --git a/src/g_level.cpp b/src/g_level.cpp
index b811c1215..01911f742 100644
--- a/src/g_level.cpp
+++ b/src/g_level.cpp
@@ -427,6 +427,7 @@ void G_InitNew (const char *mapname, bool bTitleLevel)
 	UnlatchCVars ();
 	G_VerifySkill();
 	UnlatchCVars ();
+	DThinker::DestroyThinkersInList(STAT_STATIC);
 
 	if (paused)
 	{
diff --git a/src/p_actionfunctions.cpp b/src/p_actionfunctions.cpp
index 8f916614b..16c8c3267 100644
--- a/src/p_actionfunctions.cpp
+++ b/src/p_actionfunctions.cpp
@@ -1124,7 +1124,7 @@ DEFINE_ACTION_FUNCTION(AActor, A_SeekerMissile)
 	PARAM_INT_DEF(chance);
 	PARAM_INT_DEF(distance);
 
-	if ((flags & SMF_LOOK) && (self->tracer == 0) && (pr_seekermissile()<chance))
+	if ((flags & SMF_LOOK) && (self->tracer == nullptr) && (pr_seekermissile()<chance))
 	{
 		self->tracer = P_RoughMonsterSearch (self, distance, true);
 	}
diff --git a/src/p_setup.cpp b/src/p_setup.cpp
index ac7faea76..308054a8b 100644
--- a/src/p_setup.cpp
+++ b/src/p_setup.cpp
@@ -4202,6 +4202,7 @@ void P_Init ()
 static void P_Shutdown ()
 {
 	// [ZZ] delete global event handlers
+	DThinker::DestroyThinkersInList(STAT_STATIC);
 	E_Shutdown(false);
 	P_DeinitKeyMessages ();
 	P_FreeLevelData ();
diff --git a/src/statnums.h b/src/statnums.h
index 7f691e232..dd868bbe1 100644
--- a/src/statnums.h
+++ b/src/statnums.h
@@ -45,6 +45,7 @@ enum
 	STAT_AUTODECAL,							// A decal that can be automatically deleted
 	STAT_CORPSEPOINTER,						// An entry in Hexen's corpse queue
 	STAT_TRAVELLING,						// An actor temporarily travelling to a new map
+	STAT_STATIC,							// persistent across maps.
 
   // Thinkers that do think
 	STAT_FIRST_THINKING=32,