diff --git a/crates/aldabra-core/src/plutus_mint.rs b/crates/aldabra-core/src/plutus_mint.rs
index aed6e88..e7b6da6 100644
--- a/crates/aldabra-core/src/plutus_mint.rs
+++ b/crates/aldabra-core/src/plutus_mint.rs
@@ -193,11 +193,13 @@ fn hash_to_hex_32(h: &[u8; 32]) -> String {
 
 // 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
+// (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;
+// 2026-05-08, FeeTooSmallUTxO @ 6353 lovelace short). Bumping to 256
+// got within 16 bytes on retry — still rejected. 512 is generous head-
+// room for any single-vkey case (~+22k lovelace overestimate worst-case,
+// trivial); reconsider for multi-sig where many vkey witnesses are added.
+const WITNESS_OVERHEAD_BYTES: u64 = 512;
 
 /// Build + sign a Plutus-policy mint with a fully-specified output.
 ///