--- a/test/build_sparse_tests.sh
+++ b/test/build_sparse_tests.sh
@@ -886,6 +886,9 @@
 %! load(savefile,"as_save");
 %! unlink(savefile);
 %! assert(as_save,sparse(af));
+## FIXME -- we should skip (or mark as an expected failure) the test for
+## saving sparse matrices to MAT files when using 64-bit indexing since
+## that is not implemented yet.
 %!test # save matlab
 %! savefile= tmpnam();
 %! as_save=as; save("-mat",savefile,"bf","as_save","af");