diff --git a/src/cuda/3d/spread3d_wrapper.cu b/src/cuda/3d/spread3d_wrapper.cu
index f652411f8..9ae0d4d56 100644
--- a/src/cuda/3d/spread3d_wrapper.cu
+++ b/src/cuda/3d/spread3d_wrapper.cu
@@ -191,7 +191,7 @@ int cuspread3d_nuptsdriven(int nf1, int nf2, int nf3, int M, cufinufft_plan_t<T>
     cuda_complex<T> *d_c = d_plan->c;
     cuda_complex<T> *d_fw = d_plan->fw;
 
-    threadsPerBlock.x = 64;
+    threadsPerBlock.x = 16;
     threadsPerBlock.y = 1;
     blocks.x = (M + threadsPerBlock.x - 1) / threadsPerBlock.x;
     blocks.y = 1;