diff --git a/Cura/util/util3d.py b/Cura/util/util3d.py
index 2592785..217814b 100644
--- a/Cura/util/util3d.py
+++ b/Cura/util/util3d.py
@@ -33,14 +33,14 @@ class Vector3(object):
 
 	def __iadd__(self, v):
 		self.x += v.x
-		self.y += v.x
-		self.z += v.x
+		self.y += v.y
+		self.z += v.z
 		return self
 
 	def __isub__(self, v):
 		self.x += v.x
-		self.y += v.x
-		self.z += v.x
+		self.y += v.y
+		self.z += v.z
 		return self
 
 	def __imul__(self, v):