diff --git a/src/deb/mod.rs b/src/deb/mod.rs
index 30ea365..7c76889 100644
--- a/src/deb/mod.rs
+++ b/src/deb/mod.rs
@@ -297,20 +297,29 @@ async fn build_binary_package_impl(
     // UNRELEASED is not a real archive series: without an explicit --series,
     // build against the development series of the host vendor's distribution
     // instead. An explicit --series always wins.
-    let resolved_series;
-    let series = if let Some(s) = series {
-        s
+    let mut series = if let Some(s) = series {
+        s.to_string()
     } else if crate::distro_info::is_unreleased(&package_series) {
         let dist = crate::build::env::current_vendor();
-        resolved_series = crate::distro_info::effective_series(&package_series, &dist).await?;
+        let series = crate::distro_info::effective_series(&package_series, &dist).await?;
         log::info!(
             "Changelog is UNRELEASED, building against series {}",
-            resolved_series
+            series
         );
-        resolved_series.as_str()
+        series
     } else {
-        &package_series
+        package_series.clone()
     };
+    // A changelog (or an explicit --series) may carry a suite name instead of
+    // the series codename: Debian conventionally writes 'unstable' where the
+    // series data carries 'sid'. Resolve the alias so the codename identifies
+    // the target everywhere downstream — the chroot bootstrap, the caches and
+    // the distro-info lookups all key on codenames.
+    if let Some((_, codename)) = crate::distro_info::resolve_suite_alias(&series) {
+        log::info!("Suite '{}' resolved to series {}", series, codename);
+        series = codename;
+    }
+    let series = series.as_str();
     let current_arch = crate::get_current_arch();
     let arch = arch.as_deref().unwrap_or(&current_arch);