diff --git a/lib/interscript.rb b/lib/interscript.rb
index d5483bf8..b7d4e757 100644
--- a/lib/interscript.rb
+++ b/lib/interscript.rb
@@ -82,8 +82,28 @@ def detect(source, destination, **kwargs)
       detector.call(source, destination)
     end
 
+    # Locate the interscript-maps registry yaml(s) across installed gems.
+    #
+    # rubygems 4 removed StubSpecification#files, which
+    # Gem.find_latest_files relies on, so the fast path can raise there;
+    # the fallback globs the interscript-maps gems directly (there are
+    # only ever one or two of them, so this stays cheap).
+    def locate_map_gems_yaml
+      found = begin
+        Gem.find_latest_files("interscript-maps.yaml")
+      rescue
+        nil
+      end
+      return found if found.is_a?(Array) && found.any?
+
+      Gem::Specification.latest_specs
+        .select { |spec| spec.name == "interscript-maps" }
+        .flat_map { |spec| Dir.glob(File.join(spec.full_gem_path, "**", "interscript-maps.yaml")) }
+        .uniq
+    end
+
     def map_gems
-      @map_gems ||= Gem.find_latest_files("interscript-maps.yaml").map do |i|
+      @map_gems ||= locate_map_gems_yaml.map do |i|
         [i, YAML.load_file(i)]
       end.to_h
     end
diff --git a/spec/interscript/map_gems_spec.rb b/spec/interscript/map_gems_spec.rb
new file mode 100644
index 00000000..0afd3f2f
--- /dev/null
+++ b/spec/interscript/map_gems_spec.rb
@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+require "interscript"
+require "tmpdir"
+require "fileutils"
+require "yaml"
+
+RSpec.describe Interscript do
+  describe ".locate_map_gems_yaml" do
+    it "finds the registry yaml via Gem.find_latest_files when available" do
+      Dir.mktmpdir do |dir|
+        gem_dir = File.join(dir, "gems", "interscript-maps-9.9.9")
+        FileUtils.mkdir_p(gem_dir)
+        yaml_path = File.join(gem_dir, "interscript-maps.yaml")
+        File.write(yaml_path, {"paths" => ["maps"]}.to_yaml)
+        spec = Struct.new(:name, :full_gem_path).new("interscript-maps", gem_dir)
+        allow(Gem::Specification).to receive(:latest_specs).and_return([spec])
+        allow(Gem).to receive(:find_latest_files).with("interscript-maps.yaml").and_return([yaml_path])
+        expect(Interscript.locate_map_gems_yaml).to include(yaml_path)
+      end
+    end
+
+    it "falls back to a direct gem-dir glob when Gem.find_latest_files is unavailable (rubygems 4)" do
+      Dir.mktmpdir do |dir|
+        gem_dir = File.join(dir, "gems", "interscript-maps-9.9.9")
+        FileUtils.mkdir_p(File.join(gem_dir, "maps"))
+        yaml_path = File.join(gem_dir, "interscript-maps.yaml")
+        File.write(yaml_path, {"paths" => ["maps"]}.to_yaml)
+        spec = Struct.new(:name, :full_gem_path).new("interscript-maps", gem_dir)
+        allow(Gem::Specification).to receive(:latest_specs).and_return([spec])
+        allow(Gem).to receive(:find_latest_files).with("interscript-maps.yaml")
+          .and_raise(RuntimeError, "undefined method 'files' for Gem::StubSpecification")
+        expect(Interscript.locate_map_gems_yaml).to include(yaml_path)
+      end
+    end
+  end
+end