diff --git a/src/pack.rs b/src/pack.rs
index 151515cd..52c48a5b 100644
--- a/src/pack.rs
+++ b/src/pack.rs
@@ -80,57 +80,74 @@ pub fn pack_all(
     let mut packages = Vec::with_capacity(manifest.targets.len());
 
     for (target, _) in manifest.target_package_names() {
-        let mut derived = manifest
-            .manifest_for_target(&target)
-            .with_context(|| format!("target `{target}` disappeared during packing"))?;
-        let section = manifest
-            .targets
-            .get(&target)
-            .with_context(|| format!("target `{target}` disappeared during packing"))?;
-        let source = project.join(&section.dir);
-        if !source.is_dir() {
-            bail!(
-                "target `{target}` source root `{}` is not a directory",
-                section.dir
-            );
-        }
+        packages.push(pack_target(project, manifest, &target, Some(&output))?);
+    }
+    Ok(packages)
+}
 
-        // A root target is the repository's canonical package. Older manifests
-        // named it `<package>-repository` to avoid a schema-level name clash;
-        // the emitted artifact must nevertheless use the exact root identity
-        // so `zed install org/repository-name` works as expected.
-        if section.dir == "." {
-            derived.package.name = manifest.package.name.clone();
-        } else if source.join(zed_interfaces::paths::MANIFEST_FILE).exists() {
-            bail!(
-                "target `{target}` contains its own {}; declare packages only in the repository-root manifest",
-                zed_interfaces::paths::MANIFEST_FILE
-            );
-        }
+/// Build the one artifact `pack_all` would emit for a single declared target.
+///
+/// Resolving one package must not require every sibling target to be present:
+/// a target rooted at generated output is absent from a source tag, and that
+/// alone should not make the repository's other packages unresolvable.
+pub(crate) fn pack_target(
+    project: &Path,
+    manifest: &Manifest,
+    target: &str,
+    out_dir: Option<&Path>,
+) -> Result<PackagedTarget> {
+    let output = out_dir
+        .map(Path::to_path_buf)
+        .unwrap_or_else(|| project.join(PACK_OUT_DIR));
+    let mut derived = manifest
+        .manifest_for_target(target)
+        .with_context(|| format!("target `{target}` disappeared during packing"))?;
+    let section = manifest
+        .targets
+        .get(target)
+        .with_context(|| format!("target `{target}` disappeared during packing"))?;
+    let source = project.join(&section.dir);
+    if !source.is_dir() {
+        bail!(
+            "target `{target}` source root `{}` is not a directory",
+            section.dir
+        );
+    }
 
-        let ignore_rules = crate::publish_ignore::read_rules(&source)?;
-        let staging = tempfile::tempdir().context("create target packing directory")?;
-        copy_files(&source, staging.path(), &derived, &ignore_rules)?;
-        copy_root_legal_files(project, staging.path())?;
-        fs::write(
-            staging.path().join(zed_interfaces::paths::MANIFEST_FILE),
-            derived.to_toml_string()?,
-        )?;
-
-        let packed = pack_format_with_ignore_rules(
-            staging.path(),
-            &derived,
-            Some(&output),
-            ArtifactFormat::TarGz,
-            &ignore_rules,
-        )?;
-        packages.push(PackagedTarget {
-            target: Some(target),
-            manifest: derived,
-            packed,
-        });
+    // A root target is the repository's canonical package. Older manifests
+    // named it `<package>-repository` to avoid a schema-level name clash;
+    // the emitted artifact must nevertheless use the exact root identity
+    // so `zed install org/repository-name` works as expected.
+    if section.dir == "." {
+        derived.package.name = manifest.package.name.clone();
+    } else if source.join(zed_interfaces::paths::MANIFEST_FILE).exists() {
+        bail!(
+            "target `{target}` contains its own {}; declare packages only in the repository-root manifest",
+            zed_interfaces::paths::MANIFEST_FILE
+        );
     }
-    Ok(packages)
+
+    let ignore_rules = crate::publish_ignore::read_rules(&source)?;
+    let staging = tempfile::tempdir().context("create target packing directory")?;
+    copy_files(&source, staging.path(), &derived, &ignore_rules)?;
+    copy_root_legal_files(project, staging.path())?;
+    fs::write(
+        staging.path().join(zed_interfaces::paths::MANIFEST_FILE),
+        derived.to_toml_string()?,
+    )?;
+
+    let packed = pack_format_with_ignore_rules(
+        staging.path(),
+        &derived,
+        Some(&output),
+        ArtifactFormat::TarGz,
+        &ignore_rules,
+    )?;
+    Ok(PackagedTarget {
+        target: Some(target.to_string()),
+        manifest: derived,
+        packed,
+    })
 }
 
 fn copy_files(
diff --git a/src/source_fallback.rs b/src/source_fallback.rs
index ce33d2d8..93017817 100644
--- a/src/source_fallback.rs
+++ b/src/source_fallback.rs
@@ -948,14 +948,42 @@ fn repack_tag_archive(raw: &Path, org: &str, name: &str, version: &str, dest: &P
     // checkout's untracked inputs, which a tag archive cannot contain.
     let manifest =
         crate::pack_inputs::harden_manifest(crate::pack_guard::harden_manifest(manifest));
-    let packages = crate::pack::pack_all(&tree, &manifest, Some(&staging.path().join("out")))
-        .context("repack GitHub tag archive")?;
-    let root = packages
-        .into_iter()
-        .find(|package| package.manifest.package.name == name)
-        .with_context(|| {
-            format!("GitHub tag archive for {org}/{name}@{version} publishes no root package")
+    let out = staging.path().join("out");
+    // Pack only the target that provides the requested package. Packing every
+    // declared target would fail on a sibling rooted at generated output that
+    // a source tag cannot contain, making this package unresolvable for a
+    // reason that has nothing to do with it.
+    let root = if manifest.is_polyglot() {
+        let mut selected = None;
+        for (target, target_package) in manifest.target_package_names() {
+            let is_root = manifest
+                .targets
+                .get(&target)
+                .is_some_and(|section| section.dir == ".");
+            let provided = if is_root {
+                manifest.package.name.clone()
+            } else {
+                target_package
+            };
+            if provided == name {
+                selected = Some(target);
+                break;
+            }
+        }
+        let target = selected.with_context(|| {
+            format!("GitHub tag archive for {org}/{name}@{version} publishes no such package")
         })?;
+        crate::pack::pack_target(&tree, &manifest, &target, Some(&out))
+            .context("repack GitHub tag archive")?
+    } else {
+        crate::pack::pack_all(&tree, &manifest, Some(&out))
+            .context("repack GitHub tag archive")?
+            .into_iter()
+            .find(|package| package.manifest.package.name == name)
+            .with_context(|| {
+                format!("GitHub tag archive for {org}/{name}@{version} publishes no root package")
+            })?
+    };
     // Callers hand over a store cache path whose directory may not exist yet
     // (a frozen fetch uses a fresh isolated store); `download_url` creates it
     // for the other locators, so this one must too.