diff --git a/src/hash.h b/src/hash.h
index ef4e3d8..6615710 100644
--- a/src/hash.h
+++ b/src/hash.h
@@ -14,7 +14,7 @@
 #ifndef HASH_H
 #define HASH_H
 
-//#include <bug.h>
+#include <bug.h>
 
 #include "chessdefs.h"
 
@@ -121,7 +121,7 @@ bool zobrist_verify(pos_t *pos);
  */
 static inline void tt_prefetch(hkey_t key)
 {
-//    bug_on(!hash_tt.keys);
+    bug_on(!hash_tt.keys);
     __builtin_prefetch(hash_tt.keys + (key & hash_tt.mask));
 }
 
diff --git a/src/position.h b/src/position.h
index 5676430..a3eeb67 100644
--- a/src/position.h
+++ b/src/position.h
@@ -19,7 +19,7 @@
 #include <brlib.h>
 #include <bitops.h>
 #include <struct-group.h>
-// #include <bug.h>
+#include <bug.h>
 
 #include "chessdefs.h"
 #include "hash.h"