diff --git a/lib/simd/Grid_gpu_vec.h b/lib/simd/Grid_gpu_vec.h
index 9b18ecfa..3850e403 100644
--- a/lib/simd/Grid_gpu_vec.h
+++ b/lib/simd/Grid_gpu_vec.h
@@ -36,7 +36,7 @@ Author: Peter Boyle <paboyle@ph.ed.ac.uk>
 
 namespace Grid {
 
-#define COALESCE_GRANULARITY (32) // bytes for coalesce granularity of target: Pascal, Volta
+#define COALESCE_GRANULARITY (16) // bytes for coalesce granularity of target: Pascal, Volta
 
 template<class pair>
 class GpuComplex {