diff --git a/core/gather/gatherers/css-usage.js b/core/gather/gatherers/css-usage.js
index 0aea2c6f7d02..f89069280dc2 100644
--- a/core/gather/gatherers/css-usage.js
+++ b/core/gather/gatherers/css-usage.js
@@ -36,7 +36,7 @@ class CSSUsage extends BaseGatherer {
   /**
    * @param {LH.Crdp.CSS.StyleSheetAddedEvent} event
    */
-  async _onStylesheetAdded(event) {
+  _onStylesheetAdded(event) {
     if (!this._session) throw new Error('Session not initialized');
     const styleSheetId = event.header.styleSheetId;
     const sheetPromise = this._session.sendCommand('CSS.getStyleSheetText', {styleSheetId})
@@ -98,6 +98,9 @@ class CSSUsage extends BaseGatherer {
     this._ruleUsage = coverageResponse.ruleUsage;
     session.off('CSS.styleSheetAdded', this._onStylesheetAdded);
 
+    // Ensure we finish fetching all stylesheet contents before disabling the CSS domain
+    await Promise.all(this._sheetPromises.values());
+
     await session.sendCommand('CSS.disable');
     await session.sendCommand('DOM.disable');
   }