diff --git a/Cargo.lock b/Cargo.lock
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -353,6 +353,8 @@
  "chronik-proto",
  "chronik-util",
  "cxx",
+ "hex",
+ "itertools",
  "pretty_assertions",
  "prost",
  "prost-build",
diff --git a/chronik/chronik-indexer/Cargo.toml b/chronik/chronik-indexer/Cargo.toml
--- a/chronik/chronik-indexer/Cargo.toml
+++ b/chronik/chronik-indexer/Cargo.toml
@@ -25,6 +25,12 @@
 # Bridge to C++
 cxx = "1.0"
 
+# En-/decode hex
+hex = "0.4"
+
+# Extends iterators with handy helpers
+itertools = "0.10"
+
 # Protobuf en-/decoding
 prost = "0.11"
 
diff --git a/chronik/chronik-indexer/src/query/broadcast.rs b/chronik/chronik-indexer/src/query/broadcast.rs
--- a/chronik/chronik-indexer/src/query/broadcast.rs
+++ b/chronik/chronik-indexer/src/query/broadcast.rs
@@ -12,6 +12,7 @@
 use chronik_bridge::ffi;
 use chronik_db::{db::Db, mem::Mempool};
 use chronik_proto::proto;
+use itertools::Itertools;
 use thiserror::Error;
 
 use crate::{
@@ -49,6 +50,10 @@
     /// Node rejected the tx
     #[error("400: Broadcast failed: {0}")]
     BroadcastFailed(String),
+
+    /// Validation failed, inputs not found
+    #[error("404: Validation failed: input(s) {0} not found or spent")]
+    ValidationFailed(String),
 }
 
 impl QueryBroadcast<'_> {
@@ -139,12 +144,26 @@
         let tx = TxMut::deser(&mut raw_tx.into())?;
         let mut ffi_tx = ffi::Tx::from(tx);
         let mut coins_to_uncache = Vec::new();
+        let mut not_found = Vec::new();
         self.node.bridge.lookup_spent_coins(
             &mut ffi_tx,
-            &mut vec![],
+            &mut not_found,
             &mut coins_to_uncache,
         )?;
         self.node.bridge.uncache_coins(&coins_to_uncache)?;
+        if !not_found.is_empty() {
+            let not_found_str = not_found
+                .iter()
+                .map(|outpoint| {
+                    format!(
+                        "{}:{}",
+                        hex::encode(outpoint.txid),
+                        outpoint.out_idx
+                    )
+                })
+                .join(", ");
+            return Err(ValidationFailed(not_found_str).into());
+        }
         let tx = Tx::from(ffi_tx);
         let token = if self.is_token_index_enabled {
             TxTokenData::from_unbroadcast_tx(self.db, self.mempool, &tx)?