diff --git a/libs/gds21/src/write.rs b/libs/gds21/src/write.rs
index ff06f87..6af03f4 100644
--- a/libs/gds21/src/write.rs
+++ b/libs/gds21/src/write.rs
@@ -13,20 +13,24 @@ pub struct GdsWriter<'wr> {
 impl<'wr> GdsWriter<'wr> {
     /// Create new [GdsWriter] with destination file `fname`
     pub fn open(fname: impl AsRef<Path>) -> GdsResult<Self> {
-        let file = BufWriter::new(File::create(fname)?);
-        Ok(Self::new(file))
+        Ok(Self::new(File::create(fname)?))
     }
     /// Create a new [GdsWriter] to destination `dest`
+    ///
+    /// Writes to `dest` are buffered, since records are encoded a few bytes at a time.
     pub fn new(dest: impl Write + 'wr) -> Self {
         Self {
-            dest: Box::new(dest),
+            dest: Box::new(BufWriter::new(dest)),
         }
     }
     /// Write [GdsLibrary] `lib` to our destination
     pub fn write_lib(&mut self, lib: &GdsLibrary) -> GdsResult<()> {
         // `write_lib` is our typicaly entry point when writing to file.
         // It quickly dispatches most behavior off to our implementation of the [Encode] trait.
-        self.encode_lib(lib)
+        self.encode_lib(lib)?;
+        // Flush explicitly: dropping the buffer would discard any write error.
+        self.dest.flush()?;
+        Ok(())
     }
     /// Helper to write a sequence of [GdsRecord] references
     fn write_records(&mut self, records: &[GdsRecord]) -> GdsResult<()> {
diff --git a/substrate/src/layout/convert/gds.rs b/substrate/src/layout/convert/gds.rs
index b386c32..0afd5fe 100644
--- a/substrate/src/layout/convert/gds.rs
+++ b/substrate/src/layout/convert/gds.rs
@@ -49,6 +49,10 @@ pub struct GdsExporter<'a> {
     layers: Arc<RwLock<Layers>>,
     backtrace: Vec<ErrorContext>,
     names_used: HashSet<ArcStr>,
+    /// The next suffix to try when renaming a cell with a given name.
+    ///
+    /// Every lower suffix is already in `names_used`.
+    next_suffix: HashMap<ArcStr, usize>,
     /// The top level cell.
     ///
     /// The name of this cell will be preserved.
@@ -82,6 +86,7 @@ impl SubstrateCtx {
                 layers: data.layers(),
                 backtrace: Vec::new(),
                 names_used: HashSet::with_capacity(data.layouts().cells().count()),
+                next_suffix: HashMap::new(),
                 top: None,
                 export_set: ExportSet::All,
                 names: SecondaryMap::new(),
@@ -105,6 +110,7 @@ impl SubstrateCtx {
                 layers: data.layers(),
                 backtrace: Vec::new(),
                 names_used: HashSet::with_capacity(data.layouts().cells().count()),
+                next_suffix: HashMap::new(),
                 export_set: ExportSet::for_top(&top),
                 top: Some(top),
                 names: SecondaryMap::new(),
@@ -536,13 +542,15 @@ impl<'a> GdsExporter<'a> {
     fn get_cell_name(&mut self, cell: &Arc<Cell>) -> ArcStr {
         let name = cell.name();
         let name = if self.names_used.contains(name) && !self.is_top(cell) {
-            let mut i = 1;
+            // Resume where the previous search for this name stopped. Scanning from 1
+            // every time is quadratic in the number of cells sharing a name.
+            let i = self.next_suffix.entry(name.clone()).or_insert(1);
             loop {
                 let newname = arcstr::format!("{}_{}", name, i);
+                *i += 1;
                 if !self.names_used.contains(&newname) {
                     break newname;
                 }
-                i += 1;
             }
         } else {
             name.clone()