diff --git a/src/bitset.rs b/src/bitset.rs
index 1bcc1a1..e5b2db4 100644
--- a/src/bitset.rs
+++ b/src/bitset.rs
@@ -244,7 +244,11 @@ impl<Conf: Config> BitSet<Conf> {
     ///
     /// Panics, if `index` is out of index range.
     pub fn insert(&mut self, index: usize){
-        assert!(Self::is_in_range(index), "{index} is out of index range!");
+        assert!(
+            Self::is_in_range(index),
+            "{index} is out of index range (max={})!"
+            Self::max_capacity(),
+        );
 
         // That's indices to next level
         let (level0_index, level1_index, data_index) = Self::level_indices(index);
@@ -392,4 +396,4 @@ impl<Conf: Config> LevelMasksIterExt for BitSet<Conf> {
     }    
 }
 
-impl_bitset!(impl<Conf> for ref BitSet<Conf> where Conf: Config);
\ No newline at end of file
+impl_bitset!(impl<Conf> for ref BitSet<Conf> where Conf: Config);