diff --git a/include/base/SMPFunction.h b/include/base/SMPFunction.h
index 2e06a7fe9714b664d5cc87125823fbd54231703e..ee169e6075ed685c3e462602f02f68fa47dccd71 100644
--- a/include/base/SMPFunction.h
+++ b/include/base/SMPFunction.h
@@ -339,6 +339,7 @@ public:
 	}
 	inline bool IsJumpFollowBlock(STARS_ea_t InstAddr) const { return (JumpFollowNodesSet.find(InstAddr) != JumpFollowNodesSet.end()); }
 	bool IsInStackPtrCopySet(const STARSOpndTypePtr &CurrOp);
+	bool IsDefnInStackPtrCopySet(const STARSOpndTypePtr &CurrOp, const STARS_ea_t &DefAddr) const;
 	inline bool DoesStackFrameExtendPastStackTop(void) const { return StackFrameExtendsPastStackTop; };
 	inline bool IsRegPreserved(std::size_t RegNum) const { return (PreservedRegsBitmap[RegNum] != 0); };
 
diff --git a/src/base/SMPBasicBlock.cpp b/src/base/SMPBasicBlock.cpp
index d774b5d2a3a5613a3d45182a065bf80871135727..9e4c5a0d45b546eff37af40839db228eb1c970b2 100644
--- a/src/base/SMPBasicBlock.cpp
+++ b/src/base/SMPBasicBlock.cpp
@@ -1144,28 +1144,36 @@ bool SMPBasicBlock::ComputeReachesOutSet(void) {
 
 // Add DefOp, remove previous defs of DefOp that now do not reach the end of the block.
 void SMPBasicBlock::UpdateDownExposedDefs(STARSOpndTypePtr DefOp, STARS_ea_t InstAddr) {
-#if 1
-	// Only purpose of the DownExposedDefnSet is to track stack pointer copies, so save time.
-	if (!this->GetFunc()->IsInStackPtrCopySet(DefOp))
-		return;
-#endif
+	pair<STARSOpndTypePtr, STARS_ea_t> NewDefn(DefOp, InstAddr);
 
 	// First, remove any definition of DefOp that precedes the current definition.
 	set<pair<STARSOpndTypePtr, STARS_ea_t>, LessDefinition>::iterator DEDefnIter = this->GetFirstDownExposedDefn();
 	while (DEDefnIter != this->GetLastDownExposedDefn()) {
 		STARSOpndTypePtr OldOp = DEDefnIter->first;
 		if (IsEqOpIgnoreBitwidth(OldOp, DefOp)) {
-			(void) this->DownExposedDefnSet.erase(DEDefnIter);
-			break; // save time; should never be more than one defn per DefOp in this set, unlike ReachesIn & ReachesOut
+			STARS_ea_t OldAddr = DEDefnIter->second;
+			if (OldAddr == InstAddr) { // nothing is changing
+				return;
+			}
+			else {
+				(void) this->DownExposedDefnSet.erase(DEDefnIter);
+				this->SetReachesOutStale();
+				break; // save time; should never be more than one defn per DefOp in this set, unlike ReachesIn & ReachesOut
+			}
 		}
 		else {
 			++DEDefnIter;
 		}
 	}
+
+#if 1
+	// Only purpose of the DownExposedDefnSet is to track stack pointer copies, so save time.
+	if (!this->GetFunc()->IsDefnInStackPtrCopySet(DefOp, InstAddr))
+		return;
+#endif
+
 	// Next, insert the new definition.
-	pair<STARSOpndTypePtr, STARS_ea_t> NewDefn(DefOp, InstAddr);
-	pair<set<pair<STARSOpndTypePtr, STARS_ea_t>, LessDefinition>::iterator, bool> InsertResult;
-	InsertResult = this->DownExposedDefnSet.insert(NewDefn);
+	pair<set<pair<STARSOpndTypePtr, STARS_ea_t>, LessDefinition>::iterator, bool> InsertResult = this->DownExposedDefnSet.insert(NewDefn);
 	assert(InsertResult.second);
 	this->SetReachesOutStale();
 	return;
diff --git a/src/base/SMPFunction.cpp b/src/base/SMPFunction.cpp
index 6af059222ec75bcee666c6b637b06f004b55ed42..682f55fad1b2d8ed43b2c0c7c72ab985df7debb8 100644
--- a/src/base/SMPFunction.cpp
+++ b/src/base/SMPFunction.cpp
@@ -3722,6 +3722,35 @@ bool SMPFunction::IsInStackPtrCopySet(const STARSOpndTypePtr &CurrOp) {
 	return found;
 } // end of SMPFunction::IsInStackPtrCopySet()
 
+// Is definition CurrOp at DefAddr in the StackPtrCopySet, with any stack offset associated with it?
+bool SMPFunction::IsDefnInStackPtrCopySet(const STARSOpndTypePtr &CurrOp, const STARS_ea_t &DefAddr) const {
+	if (nullptr == CurrOp)
+		return false;
+
+	bool found = false;
+	// Set is composed of triples, so we have to iterate through it and compare operands.
+	set<pair<STARSOpndTypePtr, pair<STARS_ea_t, STARS_sval_t> >, LessStackDeltaCopy>::const_iterator CopyIter;
+	for (CopyIter = this->StackPtrCopySet.begin(); CopyIter != this->StackPtrCopySet.end(); ++CopyIter) {
+		pair<STARSOpndTypePtr, pair<STARS_ea_t, STARS_sval_t> > CurrCopy = *CopyIter;
+		STARSOpndTypePtr CopyOp = CurrCopy.first;
+		if (IsEqOp(CopyOp, CurrOp)) {
+			STARS_ea_t CopyAddr = CurrCopy.second.first;
+			if (CopyAddr == DefAddr) {
+				// Found it.
+				found = true;
+				break;
+			}
+		}
+		else if (CopyOp->GetOpType() > CurrOp->GetOpType()) {
+			// already moved past its spot; not found
+			break;
+		}
+	}
+
+	return found;
+} // end of SMPFunction::IsDefnInStackPtrCopySet()
+
+
 // Find evidence of calls to alloca(), which appear as stack space allocations (i.e.
 //  subtractions [of unknown values(?)] from the stack pointer) AFTER the local frame allocation instruction
 //  for this function.