diff --git a/taichi/program/sparse_matrix.cpp b/taichi/program/sparse_matrix.cpp
index 76044953b01c74..3e00a33f13f774 100644
--- a/taichi/program/sparse_matrix.cpp
+++ b/taichi/program/sparse_matrix.cpp
@@ -257,7 +257,7 @@ void CuSparseMatrix::spmv(Program *prog, const Ndarray &x, Ndarray &y) {
 
   void *dBuffer = NULL;
   CUDAContext::get_instance().make_current();
-  CUDADriver::get_instance().malloc(&dBuffer, 8);
+  CUDADriver::get_instance().malloc(&dBuffer, bufferSize);
   printf("spmv bufferSize: %zu\n", bufferSize);
   CUSPARSEDriver::get_instance().cpSpMV(
       cusparse_handle, CUSPARSE_OPERATION_NON_TRANSPOSE, &alpha, matrix_, vecX,