diff --git a/libspu/mpc/cheetah/ot/basic_ot_prot.cc b/libspu/mpc/cheetah/ot/basic_ot_prot.cc
index 29fe5f96..201a57ad 100644
--- a/libspu/mpc/cheetah/ot/basic_ot_prot.cc
+++ b/libspu/mpc/cheetah/ot/basic_ot_prot.cc
@@ -74,15 +74,15 @@ NdArrayRef BasicOTProtocols::PackedB2A(const NdArrayRef &inp) {
   const int64_t n = inp.numel();
   size_t nbits = share_t->nbits() == 0 ? 1 : share_t->nbits();
   if (n >= 8) {
-    // 8bits-align
+    // 8bits-align for a larger input
     nbits = (nbits + 7) / 8 * 8;
   }
   SPU_ENFORCE(nbits > 0 && nbits <= 8 * SizeOf(field));
 
   auto rand_bits = DISPATCH_ALL_FIELDS(field, "single_b2a", [&]() {
-    if ((n * inp.elsize()) & 7) {
-      // The SseTranspose requires the #columns is multiple of 8
-      // Thus, we call the less efficient RandBits.
+    if ((nbits & 7) or (n * inp.elsize()) & 7) {
+      //  The SseTranspose requires the #rows and #columns is multiple of 8.
+      //  Thus, we call the less efficient RandBits on margin cases.
       return RandBits(field, {static_cast<int64_t>(n * nbits)});
     }
 
diff --git a/libspu/mpc/cheetah/ot/basic_ot_prot_test.cc b/libspu/mpc/cheetah/ot/basic_ot_prot_test.cc
index 09fbb4df..aa18321c 100644
--- a/libspu/mpc/cheetah/ot/basic_ot_prot_test.cc
+++ b/libspu/mpc/cheetah/ot/basic_ot_prot_test.cc
@@ -129,10 +129,10 @@ TEST_P(BasicOTProtTest, SingleB2A) {
 
 TEST_P(BasicOTProtTest, PackedB2A) {
   size_t kWorldSize = 2;
-  Shape shape = {11, 12, 13};
+  Shape shape = {2};
   FieldType field = std::get<0>(GetParam());
   auto ot_type = std::get<1>(GetParam());
-  for (size_t nbits : {8}) {
+  for (size_t nbits : {3, 8, 9}) {
     size_t packed_nbits = nbits;
     auto boolean_t = makeType<BShrTy>(field, packed_nbits);