diff --git a/crates/aldabra-core/src/plutus_mint.rs b/crates/aldabra-core/src/plutus_mint.rs
index 658d489..aed6e88 100644
--- a/crates/aldabra-core/src/plutus_mint.rs
+++ b/crates/aldabra-core/src/plutus_mint.rs
@@ -191,7 +191,13 @@ fn hash_to_hex_32(h: &[u8; 32]) -> String {
     s
 }
 
-const WITNESS_OVERHEAD_BYTES: u64 = 128;
+// Generous overhead for the vkey witness + redeemer ex_units inflation +
+// CBOR length-prefix flips between unsigned (def-length) and signed
+// (indef-length) array tags. Original 128 underbid by ~144 bytes on a
+// 3-input + inline-V2-policy mint (preprod_test2 governor bootstrap
+// 2026-05-08, FeeTooSmallUTxO @ 6353 lovelace short). 256 is plenty
+// for any single-vkey signing case.
+const WITNESS_OVERHEAD_BYTES: u64 = 256;
 
 /// Build + sign a Plutus-policy mint with a fully-specified output.
 ///