diff --git a/src/search.cpp b/src/search.cpp
index 8b3b8fb4864..1aa3e92e694 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -557,7 +557,7 @@ namespace {
     // search to overwrite a previous full search TT value, so we use a different
     // position key in case of an excluded move.
     excludedMove = ss->excludedMove;
-    posKey = pos.key() ^ Key(excludedMove);
+    posKey = pos.key() ^ Key(excludedMove << 16); // isn't a very good hash
     tte = TT.probe(posKey, ttHit);
     ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
     ttMove =  rootNode ? thisThread->rootMoves[thisThread->PVIdx].pv[0]
diff --git a/src/tt.cpp b/src/tt.cpp
index f283d0c6d71..a1ef4442283 100644
--- a/src/tt.cpp
+++ b/src/tt.cpp
@@ -33,7 +33,7 @@ TranspositionTable TT; // Our global transposition table
 
 void TranspositionTable::resize(size_t mbSize) {
 
-  size_t newClusterCount = size_t(1) << msb((mbSize * 1024 * 1024) / sizeof(Cluster));
+  size_t newClusterCount = mbSize * 1024 * 1024 / sizeof(Cluster);
 
   if (newClusterCount == clusterCount)
       return;
diff --git a/src/tt.h b/src/tt.h
index 24045ed0f40..e1bef323af5 100644
--- a/src/tt.h
+++ b/src/tt.h
@@ -104,9 +104,9 @@ class TranspositionTable {
   void resize(size_t mbSize);
   void clear();
 
-  // The lowest order bits of the key are used to get the index of the cluster
+  // The 32 lowest order bits of the key are used to get the index of the cluster
   TTEntry* first_entry(const Key key) const {
-    return &table[(size_t)key & (clusterCount - 1)].entry[0];
+    return &table[(uint32_t(key) * uint64_t(clusterCount)) >> 32].entry[0];
   }
 
 private:
diff --git a/src/ucioption.cpp b/src/ucioption.cpp
index b902677f93c..f85ede1813c 100644
--- a/src/ucioption.cpp
+++ b/src/ucioption.cpp
@@ -55,7 +55,8 @@ bool CaseInsensitiveLess::operator() (const string& s1, const string& s2) const
 
 void init(OptionsMap& o) {
 
-  const int MaxHashMB = Is64Bit ? 1024 * 1024 : 2048;
+  // at most 2^32 clusters.
+  const int MaxHashMB = Is64Bit ? 131072 : 2048;
 
   o["Debug Log File"]        << Option("", on_logger);
   o["Contempt"]              << Option(0, -100, 100);