diff --git a/lib/annotate_rb/model_annotator/related_files_list_builder.rb b/lib/annotate_rb/model_annotator/related_files_list_builder.rb
index 0b6024a9..d61f5d3f 100644
--- a/lib/annotate_rb/model_annotator/related_files_list_builder.rb
+++ b/lib/annotate_rb/model_annotator/related_files_list_builder.rb
@@ -88,8 +88,33 @@ def related_files_for_pattern(pattern_type)
 
         patterns
           .map { |f| FileNameResolver.call(f, @model_name, @table_name) }
-          .map { |f| Dir.glob(f) }
-          .flatten
+          .flat_map { |f| Dir.glob(f) }
+          .select { |f| owning_root_dir(f) == model_root_dir }
+      end
+
+      def model_root_dir
+        return @model_root_dir if defined?(@model_root_dir)
+
+        @model_root_dir = owning_root_dir(@file)
+      end
+
+      # Patterns are expanded for every `root_dir` and resolved by model name alone, so models sharing a
+      #   file basename across root directories (e.g. packwerk packs) glob the same related files. Root
+      #   directories can be nested, so a file belongs to the most specific one containing it, and only
+      #   models from that same root directory may annotate it. Returns nil for the project root.
+      def owning_root_dir(file)
+        expanded_file = File.expand_path(file)
+
+        expanded_root_dirs
+          .select { |dir| expanded_file.start_with?("#{dir}/") }
+          .max_by(&:length)
+      end
+
+      def expanded_root_dirs
+        @expanded_root_dirs ||= Array(@options[:root_dir])
+          .reject { |root_dir| root_dir.to_s.empty? }
+          .flat_map { |root_dir| Dir.glob(root_dir) }
+          .map { |root_dir| File.expand_path(root_dir) }
       end
 
       def add_related_test_files
diff --git a/spec/lib/annotate_rb/model_annotator/related_files_list_builder_spec.rb b/spec/lib/annotate_rb/model_annotator/related_files_list_builder_spec.rb
index f86b2cff..6b198779 100644
--- a/spec/lib/annotate_rb/model_annotator/related_files_list_builder_spec.rb
+++ b/spec/lib/annotate_rb/model_annotator/related_files_list_builder_spec.rb
@@ -441,5 +441,48 @@
         expect(subject).to eq([[relative_file_path, position_key]])
       end
     end
+
+    context "when models in different root directories share a file basename", :isolated_environment do
+      let(:options) do
+        AnnotateRb::Options.new(**include_nothing_options.merge(
+          {
+            exclude_tests: false,
+            root_dir: ["", "packs/*"],
+            additional_file_patterns: ["packs/*/test/models/%MODEL_NAME_WITHOUT_NS%_test.rb"]
+          }
+        ))
+      end
+
+      let(:root_test_file) { "test/models/address_test.rb" }
+      let(:pack_test_file) { "packs/contacts/test/models/address_test.rb" }
+
+      before do
+        FileUtils.mkdir_p("test/models")
+        FileUtils.touch(root_test_file)
+
+        FileUtils.mkdir_p("packs/contacts/test/models")
+        FileUtils.touch(pack_test_file)
+      end
+
+      context "when the model is in the project root" do
+        let(:file) { "app/models/address.rb" }
+        let(:model_name) { "address" }
+        let(:table_name) { "addresses" }
+
+        it "returns only the test file in the project root" do
+          expect(subject).to eq([[root_test_file, :position_in_test]])
+        end
+      end
+
+      context "when the model is in a pack" do
+        let(:file) { "packs/contacts/app/public/models/address.rb" }
+        let(:model_name) { "contacts/address" }
+        let(:table_name) { "contact_addresses" }
+
+        it "returns only the test file in its own pack" do
+          expect(subject).to eq([[pack_test_file, :position_in_additional_file_patterns]])
+        end
+      end
+    end
   end
 end