diff --git a/src/branch_and_bound.rs b/src/branch_and_bound.rs
index 75940d3..9cb51b9 100644
--- a/src/branch_and_bound.rs
+++ b/src/branch_and_bound.rs
@@ -138,7 +138,7 @@ pub fn select_coins_bnb(
 ) -> Option<std::vec::IntoIter<&WeightedUtxo>> {
     // Total_Tries in Core:
     // https://github.com/bitcoin/bitcoin/blob/1d9da8da309d1dbf9aef15eb8dc43b4a2dc3d309/src/wallet/coinselection.cpp#L74
-    const ITERATION_LIMIT: i32 = 100_000;
+    const ITERATION_LIMIT: i32 = 200_000;
 
     let mut iteration = 0;
     let mut index = 0;
@@ -179,6 +179,7 @@ pub fn select_coins_bnb(
     }
 
     while iteration < ITERATION_LIMIT {
+        println!("{} {:?}", iteration, index_selection);
         backtrack = false;
 
         // * If any of the conditions are met, backtrack.
@@ -310,6 +311,8 @@ mod tests {
     use bitcoin::TxOut;
     use bitcoin::Weight;
     use core::str::FromStr;
+    use std::iter::once;
+    use std::iter::zip;
 
     fn create_weighted_utxos(fee: Amount) -> Vec<WeightedUtxo> {
         let amts = [
@@ -719,4 +722,122 @@ mod tests {
         assert_eq!(list[1].utxo.value, Amount::from_str("6 cBTC").unwrap());
         assert_eq!(list[2].utxo.value, Amount::from_str("2 cBTC").unwrap());
     }
+
+    #[test]
+    fn select_coins_bnb_exhaust() {
+        // Recreate make_hard from bitcoin core test suit.
+        // Takes 327,661 to find a solution.
+        let base: usize = 2;
+        let alpha = (0..17).enumerate().map(|(i, _)| base.pow(17 + i as u32));
+        let target = Amount::from_sat(alpha.clone().sum::<usize>() as u64);
+
+        let beta = (0..17).enumerate().map(|(i, _)| {
+            let a = base.pow(17 + i as u32);
+            let b = base.pow(16 - i as u32);
+            a + b
+        });
+
+        let vals: Vec<_> = zip(alpha, beta)
+            // flatten requires iterable types.
+            // use once() to make tuple iterable.
+            .flat_map(|tup| once(tup.0).chain(once(tup.1)))
+            .map(|a| Amount::from_sat(a as u64))
+            .collect();
+
+        let weighted_utxos = create_weighted_utxos_from_values(vals);
+        let list = select_coins_bnb(
+            target,
+            Amount::ONE_SAT,
+            FeeRate::ZERO,
+            FeeRate::ZERO,
+            &weighted_utxos,
+        );
+
+        assert!(list.is_none());
+    }
+
+    #[test]
+    fn select_coins_bnb_exhaust_v2() {
+        // Takes 163,819 iterations to find a solution.
+        let base: usize = 2;
+        let mut target = 0;
+        let vals = (0..15)
+            .enumerate()
+            .flat_map(|(i, _)| {
+                let a = base.pow(15 + i as u32) as u64;
+                target += a;
+                vec![a, a + 2]
+            });
+
+        let vals: Vec<_> = vals.map(Amount::from_sat).collect();
+        let weighted_utxos = create_weighted_utxos_from_values(vals);
+        let list = select_coins_bnb(
+            Amount::from_sat(target),
+            Amount::ONE_SAT,
+            FeeRate::ZERO,
+            FeeRate::ZERO,
+            &weighted_utxos,
+        );
+
+        assert!(list.is_none());
+    }
+
+    #[test]
+    fn select_coins_bnb_exhaust_v3() {
+        // Takes 163,819 iterations to find a solution.
+        let base: usize = 2;
+        let mut target = 0;
+        let vals = (0..3)
+            .enumerate()
+            .flat_map(|(i, _)| {
+                let a = base.pow(4 + i as u32) as u64;
+                target += a;
+                vec![a, a + 2]
+            });
+
+        let vals: Vec<_> = vals.map(Amount::from_sat).collect();
+        let weighted_utxos = create_weighted_utxos_from_values(vals);
+        let list = select_coins_bnb(
+            Amount::from_sat(target),
+            Amount::ONE_SAT,
+            FeeRate::ZERO,
+            FeeRate::ZERO,
+            &weighted_utxos,
+        );
+
+        assert!(list.is_none());
+    }
+
+    #[test]
+    fn select_coins_bnb_exhaust_v4() {
+        // Recreate make_hard from bitcoin core test suit.
+        // Takes 327,661 to find a solution.
+        let base: usize = 2;
+        let alpha = (0..4).enumerate().map(|(i, _)| base.pow(17 + i as u32));
+        let target = Amount::from_sat(alpha.clone().sum::<usize>() as u64);
+
+        let beta = (0..4).enumerate().map(|(i, _)| {
+            let a = base.pow(4 + i as u32);
+            let b = base.pow(3 - i as u32);
+            a + b
+        });
+
+        let vals: Vec<_> = zip(alpha, beta)
+            // flatten requires iterable types.
+            // use once() to make tuple iterable.
+            .flat_map(|tup| once(tup.0).chain(once(tup.1)))
+            .map(|a| Amount::from_sat(a as u64))
+            .collect();
+
+        let weighted_utxos = create_weighted_utxos_from_values(vals);
+        let list = select_coins_bnb(
+            target,
+            Amount::ONE_SAT,
+            FeeRate::ZERO,
+            FeeRate::ZERO,
+            &weighted_utxos,
+        );
+
+        assert!(list.is_none());
+    }
 }