diff --git a/Makefile b/Makefile
index 77119c4..3effa97 100644
--- a/Makefile
+++ b/Makefile
@@ -11,8 +11,8 @@
 #
 
 SHELL     := /bin/bash
-#CC        := gcc
-CC        := gcc-13
+CC        := gcc
+#CC        := gcc-13
 #CC        := clang
 BEAR      := bear
 TOUCH     := touch
@@ -69,8 +69,9 @@ CPPFLAGS  += -DBUG_ON                                       # brlib bug.h
 # fen.c
 #CPPFLAGS  += -DDEBUG_FEN                                    # FEN decoding
 
-# hash.c
-CPPFLAGS  += -DZOBRIST_VERIFY                                # chk zobrist consistency
+# hash / TT
+#CPPFLAGS  += -DZOBRIST_VERIFY                                # double chk zobrist
+#CPPFLAGS  += -DPERFT_MOVE_HISTORY			      # perft, keep prev moves
 
 # attack.c
 #CPPFLAGS  += -DDEBUG_ATTACK_ATTACKERS                       # sq_attackers
diff --git a/src/hash.h b/src/hash.h
index 2ebb145..7119bd1 100644
--- a/src/hash.h
+++ b/src/hash.h
@@ -93,7 +93,7 @@ typedef struct {
  * we use the formula:
  * idx = ( ( ep & SQUARE_NONE ) >> 3 ) | sq_file(ep);
  */
-#define EP_ZOBRIST_IDX(ep) ( ( (ep) >> 3 ) | sq_file(ep) )
+#define EP_ZOBRIST_IDX(ep) ( ( ( ep & SQUARE_NONE ) >> 3 ) | sq_file(ep) )
 
 extern hkey_t zobrist_pieces[16][64];
 extern hkey_t zobrist_castling[4 * 4 + 1];