1 files changed, 1 insertions, 1 deletions
diff --git a/puzzle.cpp b/puzzle.cpp
index fa181aa..11b2693 100644
--- a/puzzle.cpp
+++ b/puzzle.cpp
@@ -346,7 +346,7 @@ unsigned int Puzzle::numbers_count(Pos pos) const
 bool Puzzle::possible_number(Pos pos, unsigned int number) const
 {
   assert(pos <= Pos::last());
-  assert(0 <= number && number <= DIM);
+  assert(0 < number && number <= DIM);
   return numbers[pos][number];
 }