diff --git a/karma.conf.ts b/karma.conf.ts
index c10ac4b33..802b77af0 100644
--- a/karma.conf.ts
+++ b/karma.conf.ts
@@ -42,6 +42,7 @@ module.exports = (config: Config): void => {
             'nimma/fallbacks': require.resolve('./node_modules/nimma/dist/legacy/cjs/fallbacks/index.js'),
             'nimma/legacy': require.resolve('./node_modules/nimma/dist/legacy/cjs/index.js'),
             'node-fetch': require.resolve('./__karma__/fetch'),
+            '^rollup$': 'rollup/dist/rollup.browser.js',
             fs: require.resolve('./__karma__/fs'),
             process: require.resolve('./__mocks__/process'),
             perf_hooks: require.resolve('./__karma__/perf_hooks'),
diff --git a/packages/ruleset-bundler/src/plugins/virtualFs.ts b/packages/ruleset-bundler/src/plugins/virtualFs.ts
index 6c64d851d..f5e737899 100644
--- a/packages/ruleset-bundler/src/plugins/virtualFs.ts
+++ b/packages/ruleset-bundler/src/plugins/virtualFs.ts
@@ -1,9 +1,9 @@
 import { dirname, parse, join, normalize, isAbsolute, isURL } from '@stoplight/path';
-import type { Plugin, PluginContext } from 'rollup';
+import type { Plugin } from 'rollup';
 import type { IO } from '../types';
 
 export const virtualFs = ({ fs }: IO): Plugin => {
-  const recognized = new WeakMap<PluginContext, string[]>();
+  const recognized = new Set();
 
   return {
     name: '@stoplight-spectral/virtual-fs',
@@ -27,18 +27,12 @@ export const virtualFs = ({ fs }: IO): Plugin => {
         resolvedSource = join(dirname(importer), source);
       }
 
-      let existingEntries = recognized.get(this);
-      if (existingEntries === void 0) {
-        existingEntries = [];
-        recognized.set(this, existingEntries);
-      }
-
-      existingEntries.push(resolvedSource);
+      recognized.add(resolvedSource);
 
       return resolvedSource;
     },
     load(id): Promise<string> | undefined {
-      if (!isURL(id) && recognized.get(this)?.includes(id) === true) {
+      if (!isURL(id) && recognized.has(id)) {
         return fs.promises.readFile(id, 'utf8');
       }