diff --git a/src/3rdparty/squirrel/squirrel/sqcompiler.cpp b/src/3rdparty/squirrel/squirrel/sqcompiler.cpp
index 9eb71d457fe88..00e5df04f49ae 100644
--- a/src/3rdparty/squirrel/squirrel/sqcompiler.cpp
+++ b/src/3rdparty/squirrel/squirrel/sqcompiler.cpp
@@ -836,6 +836,7 @@ class SQCompiler
 			SQInteger val = _fs->PopTarget();
 			SQInteger key = _fs->PopTarget();
 			SQInteger attrs = hasattrs ? _fs->PopTarget():-1;
+			(void)attrs; // assert only
 			assert((hasattrs && attrs == key-1) || !hasattrs);
 			unsigned char flags = (hasattrs?NEW_SLOT_ATTRIBUTES_FLAG:0)|(isstatic?NEW_SLOT_STATIC_FLAG:0);
 			SQInteger table = _fs->TopTarget(); //<<BECAUSE OF THIS NO COMMON EMIT FUNC IS POSSIBLE
diff --git a/src/3rdparty/squirrel/squirrel/sqstate.cpp b/src/3rdparty/squirrel/squirrel/sqstate.cpp
index 35878e197b6c5..89dce7328fbc9 100644
--- a/src/3rdparty/squirrel/squirrel/sqstate.cpp
+++ b/src/3rdparty/squirrel/squirrel/sqstate.cpp
@@ -252,7 +252,9 @@ SQInteger SQSharedState::CollectGarbage(SQVM *vm)
 	SQVM *vms = _thread(_root_vm);
 
 	vms->Mark(&tchain);
+#ifndef NDEBUG
 	SQInteger x = _table(_thread(_root_vm)->_roottable)->CountUsed();
+#endif
 	_refs_table.Mark(&tchain);
 	MarkObject(_registry,&tchain);
 	MarkObject(_consts,&tchain);
@@ -289,7 +291,9 @@ SQInteger SQSharedState::CollectGarbage(SQVM *vm)
 		t = t->_next;
 	}
 	_gc_chain = tchain;
+#ifndef NDEBUG
 	SQInteger z = _table(_thread(_root_vm)->_roottable)->CountUsed();
+#endif
 	assert(z == x);
 	return n;
 }
diff --git a/src/3rdparty/squirrel/squirrel/sqvm.cpp b/src/3rdparty/squirrel/squirrel/sqvm.cpp
index ee1acbf32824c..5419c94cf02b6 100644
--- a/src/3rdparty/squirrel/squirrel/sqvm.cpp
+++ b/src/3rdparty/squirrel/squirrel/sqvm.cpp
@@ -1471,8 +1471,8 @@ bool SQVM::DeleteSlot(const SQObjectPtr &self,const SQObjectPtr &key,SQObjectPtr
 
 bool SQVM::Call(SQObjectPtr &closure,SQInteger nparams,SQInteger stackbase,SQObjectPtr &outres,SQBool raiseerror,SQBool can_suspend)
 {
-#ifdef _DEBUG
-SQInteger prevstackbase = _stackbase;
+#ifndef NDEBUG
+	SQInteger prevstackbase = _stackbase;
 #endif
 	switch(type(closure)) {
 	case OT_CLOSURE: {
@@ -1504,7 +1504,7 @@ SQInteger prevstackbase = _stackbase;
 	default:
 		return false;
 	}
-#ifdef _DEBUG
+#ifndef NDEBUG
 	if(!_suspended) {
 		assert(_stackbase == prevstackbase);
 	}
diff --git a/src/blitter/factory.hpp b/src/blitter/factory.hpp
index c76126fb598ed..94f3f99988139 100644
--- a/src/blitter/factory.hpp
+++ b/src/blitter/factory.hpp
@@ -61,13 +61,14 @@ class BlitterFactory {
 			name(name), description(description)
 	{
 		if (usable) {
+			Blitters &blitters = GetBlitters();
+			assert(blitters.find(this->name) == blitters.end());
 			/*
 			 * Only add when the blitter is usable. Do not bail out or
 			 * do more special things since the blitters are always
 			 * instantiated upon start anyhow and freed upon shutdown.
 			 */
-			std::pair<Blitters::iterator, bool> P = GetBlitters().insert(Blitters::value_type(this->name, this));
-			assert(P.second);
+			blitters.insert(Blitters::value_type(this->name, this));
 		} else {
 			DEBUG(driver, 1, "Not registering blitter %s as it is not usable", name);
 		}
diff --git a/src/pathfinder/npf/npf.cpp b/src/pathfinder/npf/npf.cpp
index 5a5ff927e4e4b..315b43b0e792a 100644
--- a/src/pathfinder/npf/npf.cpp
+++ b/src/pathfinder/npf/npf.cpp
@@ -1000,9 +1000,6 @@ static void NPFFollowTrack(AyStar *aystar, OpenListNode *current)
  */
 static NPFFoundTargetData NPFRouteInternal(AyStarNode *start1, bool ignore_start_tile1, AyStarNode *start2, bool ignore_start_tile2, NPFFindStationOrTileData *target, AyStar_EndNodeCheck target_proc, AyStar_CalculateH heuristic_proc, AyStarUserData *user, uint reverse_penalty, bool ignore_reserved = false, int max_penalty = 0)
 {
-	int r;
-	NPFFoundTargetData result;
-
 	/* Initialize procs */
 	_npf_aystar.max_path_cost = max_penalty;
 	_npf_aystar.CalculateH = heuristic_proc;
@@ -1032,6 +1029,7 @@ static NPFFoundTargetData NPFRouteInternal(AyStarNode *start1, bool ignore_start
 	}
 
 	/* Initialize result */
+	NPFFoundTargetData result;
 	result.best_bird_dist = UINT_MAX;
 	result.best_path_dist = UINT_MAX;
 	result.best_trackdir  = INVALID_TRACKDIR;
@@ -1046,7 +1044,8 @@ static NPFFoundTargetData NPFRouteInternal(AyStarNode *start1, bool ignore_start
 	_npf_aystar.user_data = user;
 
 	/* GO! */
-	r = _npf_aystar.Main();
+	int r = _npf_aystar.Main();
+	(void)r; // assert only
 	assert(r != AYSTAR_STILL_BUSY);
 
 	if (result.best_bird_dist != 0) {