diff --git a/Common/helper_math.h b/Common/helper_math.h
index 6d2f63ae..6f991d73 100644
--- a/Common/helper_math.h
+++ b/Common/helper_math.h
@@ -263,27 +263,27 @@ inline __host__ __device__ uint4 make_uint4(int4 a)
 // negate
 ////////////////////////////////////////////////////////////////////////////////
 
-inline __host__ __device__ float2 operator-(float2 &a)
+inline __host__ __device__ float2 operator-(float2 a)
 {
     return make_float2(-a.x, -a.y);
 }
-inline __host__ __device__ int2 operator-(int2 &a)
+inline __host__ __device__ int2 operator-(int2 a)
 {
     return make_int2(-a.x, -a.y);
 }
-inline __host__ __device__ float3 operator-(float3 &a)
+inline __host__ __device__ float3 operator-(float3 a)
 {
     return make_float3(-a.x, -a.y, -a.z);
 }
-inline __host__ __device__ int3 operator-(int3 &a)
+inline __host__ __device__ int3 operator-(int3 a)
 {
     return make_int3(-a.x, -a.y, -a.z);
 }
-inline __host__ __device__ float4 operator-(float4 &a)
+inline __host__ __device__ float4 operator-(float4 a)
 {
     return make_float4(-a.x, -a.y, -a.z, -a.w);
 }
-inline __host__ __device__ int4 operator-(int4 &a)
+inline __host__ __device__ int4 operator-(int4 a)
 {
     return make_int4(-a.x, -a.y, -a.z, -a.w);
 }