diff --git a/internal/ceres/block_random_access_matrix.h b/internal/ceres/block_random_access_matrix.h
index f398af3..b76cb78 100644
--- a/internal/ceres/block_random_access_matrix.h
+++ b/internal/ceres/block_random_access_matrix.h
@@ -77,7 +77,7 @@
 //
 //  if (cell != NULL) {
 //     MatrixRef m(cell->values, row_stride, col_stride);
-//     MutexLock l(&cell->m);
+//     CeresMutexLock l(&cell->m);
 //     m.block(row, col, row_block_size, col_block_size) = ...
 //  }