diff --git a/rust/src/smb/files.rs b/rust/src/smb/files.rs
index 71f23a6db0..6f2f1f10db 100644
--- a/rust/src/smb/files.rs
+++ b/rust/src/smb/files.rs
@@ -113,6 +113,7 @@ impl SMBState {
             tx.id,
             String::from_utf8_lossy(file_name)
         );
+        self.file_tx_count += 1;
         self.transactions.push_back(tx);
         self.transactions.back_mut()
     }
@@ -213,18 +214,11 @@ impl SMBState {
         } else {
             self.file_tc_left
         };
-        let file_handle = if direction == Direction::ToServer {
-            self.file_ts_guid.to_vec()
-        } else {
-            self.file_tc_guid.to_vec()
-        };
-
-        let ssn_gap = self.ts_ssn_gap | self.tc_ssn_gap;
         // Backstop: cap the OOO queue on every open file tx (an interleaved
-        // handle can hide a first file's queue), running even with chunk_left == 0.
-        if ssn_gap {
-            // Last-resort cap for OOO data in gapped streams: configured
-            // size/count (1 GiB / 1024 when limits are off).
+        // handle can hide a queue); runs when the call feeds data: app-layer
+        // OOO needs no stream gap to grow a queue, an empty call grows none.
+        // A queue can only exist inside a held file tx.
+        if !data.is_empty() && self.file_tx_count > 0 {
             let backstop = Self::ooo_queue_backstop(direction);
             let cnt_backstop = Self::ooo_queue_backstop_cnt(direction);
             for tx in &mut self.transactions {
@@ -234,7 +228,7 @@ impl SMBState {
                         let queued_cnt = tdf.file_tracker.get_inflight_cnt() as u64;
                         if queued_data > backstop || queued_cnt > cnt_backstop {
                             SCLogDebug!(
-                                "QUEUED size {} / count {} > backstop {} / {} while we've seen GAPs. Truncating file.",
+                                "QUEUED size {} / count {} > backstop {} / {}. Truncating file.",
                                 queued_data,
                                 queued_cnt,
                                 backstop,
@@ -256,6 +250,13 @@ impl SMBState {
             return 0;
         }
         SCLogDebug!("chunk_left {} data {}", chunk_left, data.len());
+        // the backstop above no longer needs the handle: allocate it only
+        // when a chunk is in flight
+        let file_handle = if direction == Direction::ToServer {
+            self.file_ts_guid.to_vec()
+        } else {
+            self.file_tc_guid.to_vec()
+        };
 
         let data_to_handle_len = if chunk_left as usize >= data.len() {
             data.len()
@@ -363,6 +364,7 @@ mod tests {
 
     #[test]
     fn test_ooo_queue_backstop_thresholds() {
+        let _lock = super::SMB_CFG_TEST_LOCK.lock().unwrap();
         // defaults: 64 MiB queue caps in both directions
         assert_eq!(SMBState::ooo_queue_backstop(Direction::ToClient), 67108864);
         assert_eq!(SMBState::ooo_queue_backstop(Direction::ToServer), 67108864);
@@ -399,6 +401,7 @@ mod tests {
     #[test]
     fn test_ooo_queue_backstop_cnt_thresholds() {
         // defaults: 64 chunks in both directions
+        let _lock = super::SMB_CFG_TEST_LOCK.lock().unwrap();
         assert_eq!(SMBState::ooo_queue_backstop_cnt(Direction::ToClient), 64);
         assert_eq!(SMBState::ooo_queue_backstop_cnt(Direction::ToServer), 64);
 
diff --git a/rust/src/smb/smb.rs b/rust/src/smb/smb.rs
index 5bd9b58abf..e9bba61952 100644
--- a/rust/src/smb/smb.rs
+++ b/rust/src/smb/smb.rs
@@ -743,6 +743,10 @@ pub struct SMBState {
     /// transactions list
     pub transactions: VecDeque<SMBTransaction>,
 
+    /// file txs held in the transactions list: the OOO backstop scan is a
+    /// no-op without one, so it is skipped when this is 0
+    pub(crate) file_tx_count: u32,
+
     /// tx counter for assigning incrementing id's to tx's
     tx_id: u64,
 
@@ -814,6 +818,7 @@ impl SMBState {
             check_post_gap_file_txs: false,
             post_gap_files_checked: false,
             transactions: VecDeque::new(),
+            file_tx_count: 0,
             tx_id: 0,
             dialect: 0,
             dialect_vec: None,
@@ -863,6 +868,12 @@ impl SMBState {
             }
         }
         if found {
+            if matches!(
+                self.transactions[index].type_data,
+                Some(SMBTransactionTypeData::FILE(_))
+            ) {
+                self.file_tx_count = self.file_tx_count.saturating_sub(1);
+            }
             SCLogDebug!(
                 "freeing TX with ID {} TX.ID {} at index {} left: {} max id: {}",
                 tx_id,