diff --git a/lib/ruby_wasm/packager.rb b/lib/ruby_wasm/packager.rb
index eef6fe4fb8..4d05f84ae2 100644
--- a/lib/ruby_wasm/packager.rb
+++ b/lib/ruby_wasm/packager.rb
@@ -84,6 +84,7 @@ def root
 
   # Retrieves the alias definitions for the Ruby sources.
   def self.build_source_aliases(root)
+    # @type var sources: Hash[string, RubyWasm::Packager::build_source]
     sources = {
       "head" => {
         type: "github",
diff --git a/sig/ruby_wasm/packager.rbs b/sig/ruby_wasm/packager.rbs
index 999d147f3e..38060d6cd5 100644
--- a/sig/ruby_wasm/packager.rbs
+++ b/sig/ruby_wasm/packager.rbs
@@ -17,7 +17,7 @@ class RubyWasm::Packager
 
   def root: () -> string
 
-  type build_source = Hash[Symbol, (String | Array[String])]
+  type build_source = Hash[Symbol, (string | Array[String])]
   def self.build_source_aliases: (string root) -> Hash[string, build_source]
 
   ALL_DEFAULT_EXTS: string