diff --git a/src/BulletMultiThreaded/SpuNarrowPhaseCollisionTask/Box.h b/src/BulletMultiThreaded/SpuNarrowPhaseCollisionTask/Box.h
index a0eda8d41..a526cd9f7 100644
--- a/src/BulletMultiThreaded/SpuNarrowPhaseCollisionTask/Box.h
+++ b/src/BulletMultiThreaded/SpuNarrowPhaseCollisionTask/Box.h
@@ -17,6 +17,11 @@ subject to the following restrictions:
 #ifndef __BOX_H__
 #define __BOX_H__
 
+#ifndef PE_REF
+#define PE_REF(a) a
+#define PE_REF(a) const a&
+#endif
+
 #include <math.h>
 #include <vectormath_aos.h>
 
@@ -35,17 +40,17 @@ public:
 
 	inline Box()
 	{}
-	inline Box(Vector3 half_);
+	inline Box(PE_REF(Vector3) half_);
 	inline Box(float hx, float hy, float hz);
 
-	inline void Set(Vector3 half_);
+	inline void Set(PE_REF(Vector3) half_);
 	inline void Set(float hx, float hy, float hz);
 
 	inline Vector3 GetAABB(const Matrix3& rotation) const;
 };
 
 inline
-Box::Box(Vector3 half_)
+Box::Box(PE_REF(Vector3) half_)
 {
 	Set(half_);
 }
@@ -58,7 +63,7 @@ Box::Box(float hx, float hy, float hz)
 
 inline
 void
-Box::Set(Vector3 half_)
+Box::Set(PE_REF(Vector3) half_)
 {
 	half = half_;
 }
diff --git a/src/BulletMultiThreaded/SpuNarrowPhaseCollisionTask/boxBoxDistance.cpp b/src/BulletMultiThreaded/SpuNarrowPhaseCollisionTask/boxBoxDistance.cpp
index eba83a86f..f70b85575 100644
--- a/src/BulletMultiThreaded/SpuNarrowPhaseCollisionTask/boxBoxDistance.cpp
+++ b/src/BulletMultiThreaded/SpuNarrowPhaseCollisionTask/boxBoxDistance.cpp
@@ -115,12 +115,12 @@ VertexBFaceATest(
 	float & t0,
 	float & t1,
 	const Vector3 & hA,
-	Vector3 faceOffsetAB,
-	Vector3 faceOffsetBA,
+	PE_REF(Vector3) faceOffsetAB,
+	PE_REF(Vector3) faceOffsetBA,
 	const Matrix3 & matrixAB,
 	const Matrix3 & matrixBA,
-	Vector3 signsB,
-	Vector3 scalesB )
+	PE_REF(Vector3) signsB,
+	PE_REF(Vector3) scalesB )
 {
 	// compute a corner of box B in A's coordinate system
 
@@ -174,14 +174,18 @@ VertexBFaceATests(
 	FeatureType & featureA,
 	FeatureType & featureB,
 	const Vector3 & hA,
-	Vector3 faceOffsetAB,
-	Vector3 faceOffsetBA,
+	PE_REF(Vector3) faceOffsetAB,
+	PE_REF(Vector3) faceOffsetBA,
 	const Matrix3 & matrixAB,
 	const Matrix3 & matrixBA,
-	Vector3 signsB,
-	Vector3 scalesB,
+	PE_REF(Vector3) signsB1,
+	PE_REF(Vector3) scalesB1,
 	bool first )
 {
+	
+	Vector3 signsB = signsB1;
+	Vector3 scalesB = scalesB;
+
 	float t0, t1;
 	float distSqr;
 
@@ -247,12 +251,12 @@ VertexAFaceBTest(
 	float & t0,
 	float & t1,
 	const Vector3 & hB,
-	Vector3 faceOffsetAB,
-	Vector3 faceOffsetBA,
+	PE_REF(Vector3) faceOffsetAB,
+	PE_REF(Vector3) faceOffsetBA,
 	const Matrix3 & matrixAB,
 	const Matrix3 & matrixBA,
-	Vector3 signsA,
-	Vector3 scalesA )
+	PE_REF(Vector3) signsA,
+	PE_REF(Vector3) scalesA )
 {
 	Vector3 corner =
 		Vector3( faceOffsetBA + matrixBA.getCol0() * scalesA.getX() + matrixBA.getCol1() * scalesA.getY() );
@@ -299,14 +303,16 @@ VertexAFaceBTests(
 	FeatureType & featureA,
 	FeatureType & featureB,
 	const Vector3 & hB,
-	Vector3 faceOffsetAB,
-	Vector3 faceOffsetBA,
+	PE_REF(Vector3) faceOffsetAB,
+	PE_REF(Vector3) faceOffsetBA,
 	const Matrix3 & matrixAB,
 	const Matrix3 & matrixBA,
-	Vector3 signsA,
-	Vector3 scalesA,
+	PE_REF(Vector3) signsA1,
+	PE_REF(Vector3) scalesA1,
 	bool first )
 {
+	Vector3 signsA = signsA1;
+	Vector3 scalesA = scalesA1;
 	float t0, t1;
 	float distSqr;
 
@@ -441,14 +447,14 @@ EdgeEdgeTest_0101(
 	float & tB,
 	const Vector3 & hA,
 	const Vector3 & hB,
-	Vector3 faceOffsetAB,
-	Vector3 faceOffsetBA,
+	PE_REF(Vector3) faceOffsetAB,
+	PE_REF(Vector3) faceOffsetBA,
 	const Matrix3 & matrixAB,
 	const Matrix3 & matrixBA,
-	Vector3 signsA,
-	Vector3 signsB,
-	Vector3 scalesA,
-	Vector3 scalesB )
+	PE_REF(Vector3) signsA,
+	PE_REF(Vector3) signsB,
+	PE_REF(Vector3) scalesA,
+	PE_REF(Vector3) scalesB )
 {
 	EdgeEdgeTest( 0, X, 1, Y, 0, X, 1, Y );
 }
@@ -460,14 +466,14 @@ EdgeEdgeTest_0110(
 	float & tB,
 	const Vector3 & hA,
 	const Vector3 & hB,
-	Vector3 faceOffsetAB,
-	Vector3 faceOffsetBA,
+	PE_REF(Vector3) faceOffsetAB,
+	PE_REF(Vector3) faceOffsetBA,
 	const Matrix3 & matrixAB,
 	const Matrix3 & matrixBA,
-	Vector3 signsA,
-	Vector3 signsB,
-	Vector3 scalesA,
-	Vector3 scalesB )
+	PE_REF(Vector3) signsA,
+	PE_REF(Vector3) signsB,
+	PE_REF(Vector3) scalesA,
+	PE_REF(Vector3) scalesB )
 {
 	EdgeEdgeTest( 0, X, 1, Y, 1, Y, 0, X );
 }
@@ -479,14 +485,14 @@ EdgeEdgeTest_1001(
 	float & tB,
 	const Vector3 & hA,
 	const Vector3 & hB,
-	Vector3 faceOffsetAB,
-	Vector3 faceOffsetBA,
+	PE_REF(Vector3) faceOffsetAB,
+	PE_REF(Vector3) faceOffsetBA,
 	const Matrix3 & matrixAB,
 	const Matrix3 & matrixBA,
-	Vector3 signsA,
-	Vector3 signsB,
-	Vector3 scalesA,
-	Vector3 scalesB )
+	PE_REF(Vector3) signsA,
+	PE_REF(Vector3) signsB,
+	PE_REF(Vector3) scalesA,
+	PE_REF(Vector3) scalesB )
 {
 	EdgeEdgeTest( 1, Y, 0, X, 0, X, 1, Y );
 }
@@ -498,14 +504,14 @@ EdgeEdgeTest_1010(
 	float & tB,
 	const Vector3 & hA,
 	const Vector3 & hB,
-	Vector3 faceOffsetAB,
-	Vector3 faceOffsetBA,
+	PE_REF(Vector3) faceOffsetAB,
+	PE_REF(Vector3) faceOffsetBA,
 	const Matrix3 & matrixAB,
 	const Matrix3 & matrixBA,
-	Vector3 signsA,
-	Vector3 signsB,
-	Vector3 scalesA,
-	Vector3 scalesB )
+	PE_REF(Vector3) signsA,
+	PE_REF(Vector3) signsB,
+	PE_REF(Vector3) scalesA,
+	PE_REF(Vector3) scalesB )
 {
 	EdgeEdgeTest( 1, Y, 0, X, 1, Y, 0, X );
 }
@@ -535,16 +541,22 @@ EdgeEdgeTests(
 	FeatureType & featureB,
 	const Vector3 & hA,
 	const Vector3 & hB,
-	Vector3 faceOffsetAB,
-	Vector3 faceOffsetBA,
+	PE_REF(Vector3) faceOffsetAB,
+	PE_REF(Vector3) faceOffsetBA,
 	const Matrix3 & matrixAB,
 	const Matrix3 & matrixBA,
-	Vector3 signsA,
-	Vector3 signsB,
-	Vector3 scalesA,
-	Vector3 scalesB,
+	PE_REF(Vector3) signsA1,
+	PE_REF(Vector3) signsB1,
+	PE_REF(Vector3) scalesA1,
+	PE_REF(Vector3) scalesB1,
 	bool first )
 {
+
+	Vector3 signsA=signsA1;
+	Vector3 signsB=signsB1;
+	Vector3 scalesA=scalesA1;
+	Vector3 scalesB=scalesB1;
+
 	float distSqr;
 	float tA, tB;
 
@@ -771,8 +783,8 @@ boxBoxDistance(
 	Vector3& normal,
 	BoxPoint& boxPointA,
 	BoxPoint& boxPointB,
-	Box boxA, const Transform3& transformA,
-	Box boxB, const Transform3& transformB,
+	PE_REF(Box) boxA, const Transform3& transformA,
+	PE_REF(Box) boxB, const Transform3& transformB,
 	float distanceThreshold )
 {
 	Matrix3 identity;
diff --git a/src/BulletMultiThreaded/SpuNarrowPhaseCollisionTask/boxBoxDistance.h b/src/BulletMultiThreaded/SpuNarrowPhaseCollisionTask/boxBoxDistance.h
index c30aaf058..7e8b40f75 100644
--- a/src/BulletMultiThreaded/SpuNarrowPhaseCollisionTask/boxBoxDistance.h
+++ b/src/BulletMultiThreaded/SpuNarrowPhaseCollisionTask/boxBoxDistance.h
@@ -59,7 +59,7 @@ using namespace Vectormath::Aos;
 
 float
 boxBoxDistance(Vector3& normal, BoxPoint& boxPointA, BoxPoint& boxPointB,
-			   Box boxA, const Transform3 & transformA, Box boxB,
+			   PE_REF(Box) boxA, const Transform3 & transformA, PE_REF(Box) boxB,
 			   const Transform3 & transformB,
 			   float distanceThreshold = FLT_MAX );