diff --git a/src/engine/engine_solver.c b/src/engine/engine_solver.c
index 899d935c..7568b0f6 100644
--- a/src/engine/engine_solver.c
+++ b/src/engine/engine_solver.c
@@ -1357,7 +1357,7 @@ static mjtNum CGsearch(mjCGContext* ctx, mjtNum tolerance, mjtNum ls_iterations)
 
   // compute Mv = M * v
   mju_mulSymVecSparse(ctx->Mv, ctx->M, ctx->search, nv,
-                      ctx->M_rownnz, ctx->M_rowadr, ctx->M_diagnum, ctx->M_colind);
+                      ctx->M_rownnz, ctx->M_rowadr, ctx->M_colind);
 
   // compute Jv = J * search  (dense or sparse)
   if (!ctx->is_sparse) {
@@ -1887,7 +1887,7 @@ static void mj_solCGNewton(const mjModel* m, mjData* d, int island, int maxiter,
 
   // compute Ma = M * qacc
   mju_mulSymVecSparse(ctx.Ma, ctx.M, ctx.qacc, nv,
-                      ctx.M_rownnz, ctx.M_rowadr, ctx.M_diagnum, ctx.M_colind);
+                      ctx.M_rownnz, ctx.M_rowadr, ctx.M_colind);
 
 
   // compute Jaref = J * qacc - aref  (dense or sparse)
diff --git a/src/engine/engine_util_sparse.c b/src/engine/engine_util_sparse.c
index 8d364c5e..17e960a3 100644
--- a/src/engine/engine_util_sparse.c
+++ b/src/engine/engine_util_sparse.c
@@ -227,7 +227,7 @@ void mju_addToSymSparse(mjtNum* res, const mjtNum* mat, int n,
 void mju_mulSymVecSparse(mjtNum* restrict res, const mjtNum* restrict mat,
                          const mjtNum* restrict vec, int n,
                          const int* restrict rownnz, const int* restrict rowadr,
-                         const int* restrict diagnum, const int* restrict colind) {
+                         const int* restrict colind) {
   // clear res
   mju_zero(res, n);
 
@@ -240,13 +240,6 @@ void mju_mulSymVecSparse(mjtNum* restrict res, const mjtNum* restrict mat,
     // diagonal
     res[i] = row[diag] * vec[i];
 
-    // TODO: consider using SIMD if diagnum[i] >= 4
-
-    // shortcut for diagonal row/column
-    if (diagnum[i]) {
-      continue;
-    }
-
     // off-diagonals
     const int* ind = colind + adr;
     for (int k=diag-1; k >= 0; k--) {
diff --git a/src/engine/engine_util_sparse.h b/src/engine/engine_util_sparse.h
index 616b4d21..ab7ea0f3 100644
--- a/src/engine/engine_util_sparse.h
+++ b/src/engine/engine_util_sparse.h
@@ -64,8 +64,7 @@ MJAPI void mju_addToSymSparse(mjtNum* res, const mjtNum* mat, int n,
 // multiply symmetric matrix (only lower triangle represented) by vector:
 //  res = (mat + strict_upper(mat')) * vec
 MJAPI void mju_mulSymVecSparse(mjtNum* res, const mjtNum* mat, const mjtNum* vec, int n,
-                               const int* rownnz, const int* rowadr, const int* diagnum,
-                               const int* colind);
+                               const int* rownnz, const int* rowadr, const int* colind);
 
 // compress sparse matrix, remove elements with abs(value) <= minval, return total non-zeros
 MJAPI int mju_compressSparse(mjtNum* mat, int nr, int nc,
diff --git a/test/engine/engine_util_sparse_test.cc b/test/engine/engine_util_sparse_test.cc
index 10875a67..7fee2127 100644
--- a/test/engine/engine_util_sparse_test.cc
+++ b/test/engine/engine_util_sparse_test.cc
@@ -1075,7 +1075,7 @@ TEST_F(EngineUtilSparseTest, MjuMulSymVecSparse) {
   constexpr int nnz = 9;
 
   mjtNum mat[n*n] = {1,  0,  0,  0,
-                    -1,  2,  0,  0,  // spurious (ignored) -1 at (1, 0)
+                     0,  2,  0,  0,
                      3,  0,  4,  0,
                      5,  6,  7,  8};
 
@@ -1090,12 +1090,11 @@ TEST_F(EngineUtilSparseTest, MjuMulSymVecSparse) {
   int rowadr[n];
   int colind[nnz];
   mju_dense2sparse(mat_sparse, mat, n, n, rownnz, rowadr, colind, nnz);
-  int diagnum[n] = {0, 1, 0, 0};
 
   // multiply: res = (mat + strict_upper(mat')) * vec
   mjtNum vec[n] = {4, 3, 2, 1};
   mjtNum res[n];
-  mju_mulSymVecSparse(res, mat_sparse, vec, n, rownnz, rowadr, diagnum, colind);
+  mju_mulSymVecSparse(res, mat_sparse, vec, n, rownnz, rowadr, colind);
 
   // dense multiply
   mjtNum res2[n];