diff --git a/xs/src/clipper.cpp b/xs/src/clipper.cpp
index 83153c996..bfdcd5d98 100644
--- a/xs/src/clipper.cpp
+++ b/xs/src/clipper.cpp
@@ -542,8 +542,8 @@ bool SlopesEqual(const TEdge &e1, const TEdge &e2, bool UseFullInt64Range)
 }
 //------------------------------------------------------------------------------
 
-bool SlopesEqual(const IntPoint pt1, const IntPoint pt2,
-  const IntPoint pt3, bool UseFullInt64Range)
+bool SlopesEqual(const IntPoint &pt1, const IntPoint &pt2,
+  const IntPoint &pt3, bool UseFullInt64Range)
 {
 #ifndef use_int32
   if (UseFullInt64Range)
@@ -554,8 +554,8 @@ bool SlopesEqual(const IntPoint pt1, const IntPoint pt2,
 }
 //------------------------------------------------------------------------------
 
-bool SlopesEqual(const IntPoint pt1, const IntPoint pt2,
-  const IntPoint pt3, const IntPoint pt4, bool UseFullInt64Range)
+bool SlopesEqual(const IntPoint &pt1, const IntPoint &pt2,
+  const IntPoint &pt3, const IntPoint &pt4, bool UseFullInt64Range)
 {
 #ifndef use_int32
   if (UseFullInt64Range)
@@ -572,7 +572,7 @@ inline bool IsHorizontal(TEdge &e)
 }
 //------------------------------------------------------------------------------
 
-inline double GetDx(const IntPoint pt1, const IntPoint pt2)
+inline double GetDx(const IntPoint &pt1, const IntPoint &pt2)
 {
   return (pt1.Y == pt2.Y) ?
     HORIZONTAL : (double)(pt2.X - pt1.X) / (pt2.Y - pt1.Y);
@@ -845,8 +845,8 @@ OutPt* GetBottomPt(OutPt *pp)
 }
 //------------------------------------------------------------------------------
 
-bool Pt2IsBetweenPt1AndPt3(const IntPoint pt1,
-  const IntPoint pt2, const IntPoint pt3)
+bool Pt2IsBetweenPt1AndPt3(const IntPoint &pt1,
+  const IntPoint &pt2, const IntPoint &pt3)
 {
   if ((pt1 == pt3) || (pt1 == pt2) || (pt3 == pt2))
     return false;
@@ -1814,7 +1814,7 @@ void Clipper::CopyAELToSEL()
 }
 //------------------------------------------------------------------------------
 
-void Clipper::AddJoin(OutPt *op1, OutPt *op2, const IntPoint OffPt)
+void Clipper::AddJoin(OutPt *op1, OutPt *op2, const IntPoint &OffPt)
 {
   Join* j = new Join;
   j->OutPt1 = op1;
@@ -1840,7 +1840,7 @@ void Clipper::ClearGhostJoins()
 }
 //------------------------------------------------------------------------------
 
-void Clipper::AddGhostJoin(OutPt *op, const IntPoint OffPt)
+void Clipper::AddGhostJoin(OutPt *op, const IntPoint &OffPt)
 {
   Join* j = new Join;
   j->OutPt1 = op;
@@ -3323,7 +3323,7 @@ OutPt* DupOutPt(OutPt* outPt, bool InsertAfter)
 //------------------------------------------------------------------------------
 
 bool JoinHorz(OutPt* op1, OutPt* op1b, OutPt* op2, OutPt* op2b,
-  const IntPoint Pt, bool DiscardLeft)
+  const IntPoint &Pt, bool DiscardLeft)
 {
   Direction Dir1 = (op1->Pt.X > op1b->Pt.X ? dRightToLeft : dLeftToRight);
   Direction Dir2 = (op2->Pt.X > op2b->Pt.X ? dRightToLeft : dLeftToRight);
@@ -4462,7 +4462,7 @@ void MinkowskiSum(const Path& pattern, const Path& path, Paths& solution, bool p
 }
 //------------------------------------------------------------------------------
 
-void TranslatePath(const Path& input, Path& output, const IntPoint delta)
+void TranslatePath(const Path& input, Path& output, const IntPoint& delta)
 {
   //precondition: input != output
   output.resize(input.size());