diff --git a/CHANGELOG.md b/CHANGELOG.md
index a5f4483d..5f675975 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,8 @@
 
 ## Unreleased
 
+- fixed: Fix failed transaction processing for FIRO transactions with SparkSpend inputs.
+
 ## 3.8.7 (2025-11-05)
 
 - fixed: Added retry delay to fix dropped transaction thrashing.
diff --git a/src/common/utxobased/engine/UtxoEngineProcessor.ts b/src/common/utxobased/engine/UtxoEngineProcessor.ts
index 1c63f603..6f6b16fa 100644
--- a/src/common/utxobased/engine/UtxoEngineProcessor.ts
+++ b/src/common/utxobased/engine/UtxoEngineProcessor.ts
@@ -1354,30 +1354,44 @@ const processTransactionResponse = (
       return {
         amount: outputTotalValue,
         n: 0,
-        outputIndex: 4294967295,
+        // UINT32_MAX value, as a coinbase has no previous outpoint
+        outputIndex: 0xffffffff,
         scriptPubkey: '', // Maybe there's a bogus scriptPubkey we can use here?
         sequence: vin.sequence,
         txId: '0000000000000000000000000000000000000000000000000000000000000000'
       }
     }
 
-    if (vin.txid == null) {
-      throw new Error(`Unexpected null txid when processing transaction inputs`)
-    }
-
-    const scriptPubkey =
+    let scriptPubkey: string = 'unknown'
+    try {
       // Note: Blockbook has empirically not sent a hex value as the
       // scriptPubkey for vins. If we discover this to be changed for some
       // cases, we may want to use the `hex` field as an optimization.
-      asMaybe(
-        raw => validScriptPubkeyFromAddress(raw),
-        'unknown'
-      )({
+      scriptPubkey = validScriptPubkeyFromAddress({
         address: vin.addresses[0],
         coin: common.pluginInfo.coinInfo.name
       })
+    } catch (error) {
+      common.log.warn(
+        `failed to get scriptPubkey from address ${vin.addresses[0]}: `,
+        error
+      )
+    }
+
+    // Some inputs may not have a txid in addition to coinbase inputs, such as
+    // private transaction inputs from privacy chains (e.g. SparkSpend inputs in FIRO).
+    // Warning: Because the engine doesn't support private transactions, or any
+    // transaction outputs that wouldn't have a txid as their input in the spend transaction,
+    // we can safely assume an all-zero txid for these inputs.
+    // If we're to ever support private transaction spends, then this wouldn't
+    // be safe to assume as "our own input" because it wouldn't remove the UTXO
+    // from the DataLayer properly.
+    const txId =
+      vin.txid ??
+      '0000000000000000000000000000000000000000000000000000000000000000'
+
     return {
-      txId: vin.txid,
+      txId,
       outputIndex: vin.vout,
       n: vin.n,
       scriptPubkey,