diff --git a/CPP/Clipper2Lib/src/clipper.offset.cpp b/CPP/Clipper2Lib/src/clipper.offset.cpp
index 4b4a2218..729497c2 100644
--- a/CPP/Clipper2Lib/src/clipper.offset.cpp
+++ b/CPP/Clipper2Lib/src/clipper.offset.cpp
@@ -524,9 +524,9 @@ void ClipperOffset::DoGroupOffset(Group& group)
 void ClipperOffset::ZCB(const Point64& bot1, const Point64& top1,
 	const Point64& bot2, const Point64& top2, Point64& ip)
 {
-	if ((bot1.z != 0) && (bot1.z == bot2.z) || (bot1.z == top2.z)) ip.z = bot1.z;
-	else if ((bot2.z != 0) && (bot2.z == top1.z)) ip.z = bot2.z;
-	else if ((top1.z != 0) && (top1.z == top2.z)) ip.z = top1.z;
+	if (bot1.z && ((bot1.z == bot2.z) || (bot1.z == top2.z))) ip.z = bot1.z;
+	else if (bot2.z && (bot2.z == top1.z)) ip.z = bot2.z;
+	else if (top1.z && (top1.z == top2.z)) ip.z = top1.z;
 	else if (zCallback64_) zCallback64_(bot1, top1, bot2, top2, ip);
 }
 #endif