diff --git a/src/diff.rs b/src/diff.rs
index c348782..9dd5ff8 100644
--- a/src/diff.rs
+++ b/src/diff.rs
@@ -47,7 +47,7 @@ pub fn write_diffln<'a>(
   writer: &mut dyn fmt::Write,
   paths_old: impl Iterator<Item = &'a StorePath>,
   paths_new: impl Iterator<Item = &'a StorePath>,
-) -> fmt::Result {
+) -> Result<usize, fmt::Error> {
   let mut paths =
     FxHashMap::<&str, Diff<Vec<Option<&Version>>>>::with_hasher(FxBuildHasher);
 
@@ -105,7 +105,7 @@ pub fn write_diffln<'a>(
 
   let mut last_status = None::<DiffStatus>;
 
-  for (name, versions, status) in diffs {
+  for &(name, ref versions, status) in &diffs {
     if last_status != Some(status) {
       writeln!(
         writer,
@@ -255,5 +255,5 @@ pub fn write_diffln<'a>(
     writeln!(writer)?;
   }
 
-  Ok(())
+  Ok(diffs.len())
 }
diff --git a/src/main.rs b/src/main.rs
index 7397466..9ea86c8 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -130,7 +130,7 @@ fn real_main() -> Result<()> {
   writeln!(out)?;
 
   #[expect(clippy::pattern_type_mismatch)]
-  dix::write_diffln(
+  let wrote = dix::write_diffln(
     &mut out,
     paths_old.iter().map(|(_, path)| path),
     paths_new.iter().map(|(_, path)| path),
@@ -144,7 +144,9 @@ fn real_main() -> Result<()> {
   let size_new = size::Size::from_bytes(closure_size_new);
   let size_diff = size_new - size_old;
 
-  writeln!(out)?;
+  if wrote > 0 {
+    writeln!(out)?;
+  }
 
   writeln!(
     out,