diff --git a/cxxmph/mph_index.cc b/cxxmph/mph_index.cc
index 9e24fbd..afeae14 100644
--- a/cxxmph/mph_index.cc
+++ b/cxxmph/mph_index.cc
@@ -182,7 +182,7 @@ void MPHIndex::Ranking() {
 }
 
 uint32_t MPHIndex::Rank(uint32_t vertex) const {
-  if (!g_.size()) return 0;
+  if (!ranktable_size_) return 0;
   uint32_t index = vertex >> b_;
   uint32_t base_rank = ranktable_[index];
   uint32_t beg_idx_v = index << b_;
diff --git a/cxxmph/mph_index.h b/cxxmph/mph_index.h
index 9ab645c..dd25668 100644
--- a/cxxmph/mph_index.h
+++ b/cxxmph/mph_index.h
@@ -45,7 +45,7 @@ namespace cxxmph {
 class MPHIndex {
  public:
   MPHIndex(bool square = false, double c = 1.23, uint8_t b = 7) :
-      c_(c), b_(b), m_(0), n_(0), k_(0), square_(square), r_(1),
+      c_(c), b_(b), m_(0), n_(0), k_(0), square_(square), r_(1), g_(8, true),
       ranktable_(NULL), ranktable_size_(0) { }
   ~MPHIndex();
 
@@ -174,7 +174,6 @@ bool MPHIndex::Mapping(
 
 template <class SeededHashFcn, class Key>
 uint32_t MPHIndex::perfect_square(const Key& key) const {
-  if (!g_.size()) return 0;
   h128 h = SeededHashFcn().hash128(key, hash_seed_[0]);
   h[0] = (h[0] & (r_-1)) + nest_displacement_[0];
   h[1] = (h[1] & (r_-1)) + nest_displacement_[1];
diff --git a/cxxmph/mph_index_test.cc b/cxxmph/mph_index_test.cc
index d414bac..d0ff418 100644
--- a/cxxmph/mph_index_test.cc
+++ b/cxxmph/mph_index_test.cc
@@ -33,10 +33,11 @@ int main(int argc, char** argv) {
   cerr << endl;
   sort(ids.begin(), ids.end());
   for (vector<int>::size_type i = 0; i < ids.size(); ++i) assert(ids[i] == static_cast<vector<int>::value_type>(i));
-   /*
-  char* serialized = new char[mph_index.serialize_bytes_needed()];
-  mph_index.serialize(serialized);
-  SimpleMPHIndex<string> other_mph_index;
-  other_mph_index.deserialize(serialized);
-  */
+
+  FlexibleMPHIndex<false, true, int64_t, seeded_hash<std::hash<int64_t>>::hash_function> square_empty;
+  auto id = square_empty.index(1);
+  FlexibleMPHIndex<false, false, int64_t, seeded_hash<std::hash<int64_t>>::hash_function> unordered_empty;
+  id ^= unordered_empty.index(1);
+  FlexibleMPHIndex<true, false, int64_t, seeded_hash<std::hash<int64_t>>::hash_function> minimal_empty;
+  id ^= minimal_empty.index(1);
 }