diff --git a/src/tt.cpp b/src/tt.cpp
index 1fa60b15..1fcf8932 100644
--- a/src/tt.cpp
+++ b/src/tt.cpp
@@ -53,7 +53,7 @@ TranspositionTable::~TranspositionTable() {
 /// TranspositionTable::set_size sets the size of the transposition table,
 /// measured in megabytes.
 
-void TranspositionTable::set_size(unsigned mbSize) {
+void TranspositionTable::set_size(size_t mbSize) {
 
   assert(mbSize >= 4 && mbSize <= 8192);
 
diff --git a/src/tt.h b/src/tt.h
index c3017c64..2b2ce606 100644
--- a/src/tt.h
+++ b/src/tt.h
@@ -95,7 +95,7 @@ class TranspositionTable {
 public:
   TranspositionTable();
   ~TranspositionTable();
-  void set_size(unsigned mbSize);
+  void set_size(size_t mbSize);
   void clear();
   void store(const Key posKey, Value v, ValueType type, Depth d, Move m);
   TTEntry* retrieve(const Key posKey) const;