diff --git a/lib/ruby_lsp/addon.rb b/lib/ruby_lsp/addon.rb
index 0c1afe996..c346d6ea6 100644
--- a/lib/ruby_lsp/addon.rb
+++ b/lib/ruby_lsp/addon.rb
@@ -57,11 +57,26 @@ def load_addons(global_state, outgoing_queue, include_project_addons: true)
 
         if include_project_addons
           project_addons = Dir.glob("#{global_state.workspace_path}/**/ruby_lsp/**/addon.rb")
-
-          # Ignore add-ons from dependencies if the bundle is stored inside the project. We already found those with
-          # `Gem.find_files`
           bundle_path = Bundler.bundle_path.to_s
-          project_addons.reject! { |path| path.start_with?(bundle_path) }
+          gems_dir = Bundler.bundle_path.join("gems")
+
+          # Create an array of rejection glob patterns to ignore add-ons already discovered through Gem.find_files if
+          # they are also copied inside the workspace for whatever reason. We received reports of projects having gems
+          # installed in vendor/bundle despite BUNDLE_PATH pointing elsewhere. Without this mechanism, we will
+          # double-require the same add-on, potentially for different versions of the same gem, which leads to incorrect
+          # behavior
+          reject_glob_patterns = addon_files.map do |path|
+            relative_gem_path = Pathname.new(path).relative_path_from(gems_dir)
+            first_part, *parts = relative_gem_path.to_s.split(File::SEPARATOR)
+            first_part&.gsub!(/-([0-9.]+)$/, "*")
+            "**/#{first_part}/#{parts.join("/")}"
+          end
+
+          project_addons.reject! do |path|
+            path.start_with?(bundle_path) ||
+              reject_glob_patterns.any? { |pattern| File.fnmatch?(pattern, path, File::Constants::FNM_PATHNAME) }
+          end
+
           addon_files.concat(project_addons)
         end
 
diff --git a/test/addon_test.rb b/test/addon_test.rb
index e2efabc0a..ffadeed2b 100644
--- a/test/addon_test.rb
+++ b/test/addon_test.rb
@@ -225,5 +225,39 @@ def version
         end
       end
     end
+
+    def test_loading_project_addons_ignores_vendor_bundle
+      # Some users have gems installed under `vendor/bundle` despite not having their BUNDLE_PATH configured to be so.
+      # That leads to loading the same add-on multiple times if they have the same gem installed both in their
+      # BUNDLE_PATH and in `vendor/bundle`
+      Dir.mktmpdir do |dir|
+        addon_dir = File.join(dir, "vendor", "bundle", "rubocop-1.73.0", "lib", "ruby_lsp", "rubocop")
+        FileUtils.mkdir_p(addon_dir)
+        File.write(File.join(addon_dir, "addon.rb"), <<~RUBY)
+          class OldRuboCopAddon < RubyLsp::Addon
+            def activate(global_state, outgoing_queue)
+            end
+
+            def name
+              "Old RuboCop Addon"
+            end
+
+            def version
+              "0.1.0"
+            end
+          end
+        RUBY
+
+        @global_state.apply_options({
+          workspaceFolders: [{ uri: URI::Generic.from_path(path: dir).to_s }],
+        })
+
+        Addon.load_addons(@global_state, @outgoing_queue)
+
+        assert_raises(Addon::AddonNotFoundError) do
+          Addon.get("Project Addon", "0.1.0")
+        end
+      end
+    end
   end
 end