diff --git a/gpu/D3Q19.cu b/gpu/D3Q19.cu
index a47cdcd9..2ac09216 100644
--- a/gpu/D3Q19.cu
+++ b/gpu/D3Q19.cu
@@ -102,6 +102,7 @@ __global__  void dvc_SwapD3Q19(char *ID, double *disteven, double *distodd, int
 {
 	int i,j,k,n,nn,N;
 	// distributions
+	char id;
 	double f1,f2,f3,f4,f5,f6,f7,f8,f9;
 	double f10,f11,f12,f13,f14,f15,f16,f17,f18;
 	
@@ -111,7 +112,9 @@ __global__  void dvc_SwapD3Q19(char *ID, double *disteven, double *distodd, int
 	for (int s=0; s<S; s++){
 		//........Get 1-D index for this thread....................
 		n = S*blockIdx.x*blockDim.x + s*blockDim.x + threadIdx.x;
-		if (n<N && ID[n] > 0){
+		if (n<N){ 
+		   id = ID[n];
+		   if (id != 0){
 			//.......Back out the 3-D indices for node n..............
 			k = n/(Nx*Ny);
 			j = (n-Nx*Ny*k)/Nx;
@@ -231,6 +234,7 @@ __global__  void dvc_SwapD3Q19(char *ID, double *disteven, double *distodd, int
 			//........................................................................
 			
 		}
+		}
 	}
 }