diff --git a/oscar64/NativeCodeGenerator.cpp b/oscar64/NativeCodeGenerator.cpp
index db7e32a..05fcd27 100644
--- a/oscar64/NativeCodeGenerator.cpp
+++ b/oscar64/NativeCodeGenerator.cpp
@@ -14092,13 +14092,16 @@ bool NativeCodeBasicBlock::OptimizeXYPairUsage(void)
 
 
 
-void NativeCodeBasicBlock::BuildUseChangeSets(int start, int end, unsigned & used, unsigned & changed)
+void NativeCodeBasicBlock::BuildUseChangeSets(int start, int end, unsigned & used, unsigned & changed, uint32 & flags)
 {
 	used = 0;
 	changed = 0;
+	flags = 0;
 
 	for (int i = start; i < end; i++)
 	{
+		flags |= mIns[i].mFlags;
+
 		if (mIns[i].RequiresCarry() && !(changed & LIVE_CPU_REG_C))
 			used |= LIVE_CPU_REG_C;
 		if (mIns[i].RequiresXReg() && !(changed & LIVE_CPU_REG_X))
@@ -14118,9 +14121,13 @@ void NativeCodeBasicBlock::BuildUseChangeSets(int start, int end, unsigned & use
 bool NativeCodeBasicBlock::CanExchangeSegments(int start, int mid, int end)
 {
 	unsigned usedFront, changedFront, usedBack, changedBack;
+	uint32		flagsFront, flagsBack;
 
-	BuildUseChangeSets(start, mid, usedFront, changedFront);
-	BuildUseChangeSets(mid, end, usedBack, changedBack);
+	BuildUseChangeSets(start, mid, usedFront, changedFront, flagsFront);
+	BuildUseChangeSets(mid, end, usedBack, changedBack, flagsBack);
+
+	if (flagsFront & flagsBack & NCIF_VOLATILE)
+		return false;
 
 	if (usedFront & changedBack)
 		return false;
@@ -37788,7 +37795,7 @@ void NativeCodeProcedure::RebuildEntry(void)
 
 void NativeCodeProcedure::Optimize(void)
 {
-	CheckFunc = !strcmp(mInterProc->mIdent->mString, "check");
+	CheckFunc = !strcmp(mInterProc->mIdent->mString, "_mapUp");
 
 #if 1
 	int		step = 0;
@@ -38214,6 +38221,7 @@ void NativeCodeProcedure::Optimize(void)
 			changed = true;
 #endif
 
+
 #if 1
 		if (step >= 5)
 		{
diff --git a/oscar64/NativeCodeGenerator.h b/oscar64/NativeCodeGenerator.h
index 7fb05d0..f81e1e3 100644
--- a/oscar64/NativeCodeGenerator.h
+++ b/oscar64/NativeCodeGenerator.h
@@ -495,7 +495,7 @@ public:
 	bool MoveAccuTrainsDown(void);
 	bool MoveAccuTrainDown(int end, int start);
 
-	void BuildUseChangeSets(int start, int end, unsigned & used, unsigned & changed);
+	void BuildUseChangeSets(int start, int end, unsigned & used, unsigned & changed, uint32 & flags);
 	bool CanExchangeSegments(int start, int mid, int end);
 
 	bool CrossBlockXYPreservation(void);