diff --git a/src/scripts.rs b/src/scripts.rs
index 1152a662..e2ba7761 100644
--- a/src/scripts.rs
+++ b/src/scripts.rs
@@ -30,6 +30,10 @@ use std::{
 #[cfg(feature = "use-serde")]
 use serde::de;
 
+/// Flag applied to the nSequence and CSV value before comparing them.
+/// https://github.com/bitcoin/bitcoin/blob/4a540683ec40393d6369da1a9e02e45614db936d/src/primitives/transaction.h#L87-L89
+pub const SEQUENCE_LOCKTIME_MASK: u32 = 0x00_00_ff_ff;
+
 // These are useful to create TxOuts out of the right Script descriptor
 
 macro_rules! impl_descriptor_newtype {
@@ -135,9 +139,13 @@ macro_rules! unvault_desc_checks {
             return Err(ScriptCreationError::BadParameters);
         }
 
-        // We require the locktime to be in number of blocks, and of course to not be disabled.
+        // We require the locktime to:
+        //  - not be disabled
+        //  - be in number of blocks
+        //  - be 'clean' / minimal, ie all bits without consensus meaning should be 0
         if ($csv_value & SEQUENCE_LOCKTIME_DISABLE_FLAG) != 0
             || ($csv_value & SEQUENCE_LOCKTIME_TYPE_FLAG) != 0
+            || ($csv_value & SEQUENCE_LOCKTIME_MASK) != $csv_value
         {
             return Err(ScriptCreationError::BadParameters);
         }
diff --git a/src/transactions.rs b/src/transactions.rs
index 0fb5d7f9..5368044a 100644
--- a/src/transactions.rs
+++ b/src/transactions.rs
@@ -724,11 +724,16 @@ impl UnvaultTransaction {
     }
 
     /// Get the Unvault txo to be referenced in a spending transaction
+    ///
+    /// # Panic
+    /// Will panic if passed a csv higher than
+    /// [SEQUENCE_LOCKTIME_MASK](crate::scripts::SEQUENCE_LOCKTIME_MASK)
     pub fn spend_unvault_txin(
         &self,
         unvault_descriptor: &DerivedUnvaultDescriptor,
         csv: u32,
     ) -> UnvaultTxIn {
+        assert!(csv <= SEQUENCE_LOCKTIME_MASK, "{}", csv);
         self.unvault_txin(unvault_descriptor, csv)
     }
 
@@ -1636,7 +1641,7 @@ mod tests {
     #[test]
     fn transaction_derivation() {
         let secp = secp256k1::Secp256k1::new();
-        let csv = fastrand::u32(..1 << 22);
+        let csv = fastrand::u32(..SEQUENCE_LOCKTIME_MASK);
         eprintln!("Using a CSV of '{}'", csv);
 
         // Test the dust limit
@@ -1646,6 +1651,10 @@ mod tests {
                 .to_string(),
             Error::TransactionCreation(TransactionCreationError::Dust).to_string()
         );
+        // Non-minimal CSV
+        derive_transactions(2, 1, SEQUENCE_LOCKTIME_MASK + 1, 300_000, &secp)
+            .expect_err("Unclean CSV");
+
         // Absolute minimum
         derive_transactions(2, 1, csv, 234_632, &secp).expect(&format!(
             "Tx chain with 2 stakeholders, 1 manager, {} csv, 235_250 deposit",
@@ -1692,8 +1701,7 @@ mod tests {
             managers.len(),
             cosigners.clone(),
             csv,
-        )
-        .expect("Unvault descriptor generation error");
+        )?;
         let cpfp_descriptor =
             CpfpDescriptor::new(managers).expect("Unvault CPFP descriptor generation error");
         let deposit_descriptor =