diff --git a/lighthouse-core/test/audits/installable-manifest-test.js b/lighthouse-core/test/audits/installable-manifest-test.js
index b6af662918b5..b77cc427bf82 100644
--- a/lighthouse-core/test/audits/installable-manifest-test.js
+++ b/lighthouse-core/test/audits/installable-manifest-test.js
@@ -154,7 +154,7 @@ describe('PWA: webapp install banner audit', () => {
       return InstallableManifestAudit.audit(artifacts, context).then(result => {
         assert.strictEqual(result.score, 0);
         const items = result.details.items;
-        expect(items[0].reason).toBeDisplayString(/number of arguments/);
+        expect(items[0].reason).toMatch(/number of arguments/);
       });
     });
 
@@ -167,7 +167,7 @@ describe('PWA: webapp install banner audit', () => {
       return InstallableManifestAudit.audit(artifacts, context).then(result => {
         assert.strictEqual(result.score, 0);
         const items = result.details.items;
-        expect(items[0].reason).toBeDisplayString(/unexpected arguments/);
+        expect(items[0].reason).toMatch(/unexpected arguments/);
       });
     });
 
diff --git a/lighthouse-core/test/audits/is-on-https-test.js b/lighthouse-core/test/audits/is-on-https-test.js
index 75e6b4a30f1f..60ce36b8e820 100644
--- a/lighthouse-core/test/audits/is-on-https-test.js
+++ b/lighthouse-core/test/audits/is-on-https-test.js
@@ -84,7 +84,7 @@ describe('Security: HTTPS audit', () => {
     // Unknown blocked resolution string is used as fallback.
     expect(result.details.items[2]).toMatchObject({
       url: 'http://localhost/image2.jpeg',
-      resolution: expect.toBeDisplayString('MixedContentBlockedLOL'),
+      resolution: 'MixedContentBlockedLOL',
     });
 
     expect(result.score).toBe(0);
diff --git a/lighthouse-core/test/index-test.js b/lighthouse-core/test/index-test.js
index e05d87aee618..ae3bceb6dd57 100644
--- a/lighthouse-core/test/index-test.js
+++ b/lighthouse-core/test/index-test.js
@@ -92,8 +92,7 @@ describe('Module Tests', function() {
     try {
       await lighthouse('i-am-not-valid', {}, {});
     } catch (err) {
-      expect(err.friendlyMessage)
-          .toBeDisplayString('The URL you have provided appears to be invalid.');
+      expect(err.friendlyMessage).toBe('The URL you have provided appears to be invalid.');
       expect(err.code).toEqual('INVALID_URL');
     }
   });
@@ -103,8 +102,7 @@ describe('Module Tests', function() {
     try {
       await lighthouse('file:///a/fake/index.html', {}, {});
     } catch (err) {
-      expect(err.friendlyMessage)
-          .toBeDisplayString('The URL you have provided appears to be invalid.');
+      expect(err.friendlyMessage).toBe('The URL you have provided appears to be invalid.');
       expect(err.code).toEqual('INVALID_URL');
     }
   });
diff --git a/lighthouse-core/test/runner-test.js b/lighthouse-core/test/runner-test.js
index 3fe7ce8090a1..878cb688f031 100644
--- a/lighthouse-core/test/runner-test.js
+++ b/lighthouse-core/test/runner-test.js
@@ -790,7 +790,7 @@ describe('Runner', () => {
 
       // And it bubbled up to the runtimeError.
       expect(lhr.runtimeError.code).toEqual(NO_FCP.code);
-      expect(lhr.runtimeError.message).toBeDisplayString(/did not paint any content.*\(NO_FCP\)/);
+      expect(lhr.runtimeError.message).toMatch(/did not paint any content.*\(NO_FCP\)/);
     });
 
     it('includes a pageLoadError runtimeError over any gatherer runtimeErrors', async () => {
@@ -821,7 +821,7 @@ describe('Runner', () => {
 
       // But top-level runtimeError is the pageLoadError.
       expect(lhr.runtimeError.code).toEqual(LHError.errors.PAGE_HUNG.code);
-      expect(lhr.runtimeError.message).toBeDisplayString(/because the page stopped responding/);
+      expect(lhr.runtimeError.message).toMatch(/because the page stopped responding/);
     });
   });
 
diff --git a/lighthouse-core/test/test-utils.js b/lighthouse-core/test/test-utils.js
index 2620a1f6c4db..8b8b2ace401c 100644
--- a/lighthouse-core/test/test-utils.js
+++ b/lighthouse-core/test/test-utils.js
@@ -14,6 +14,18 @@ const {default: {toBeCloseTo}} = require('expect/build/matchers.js');
 
 expect.extend({
   toBeDisplayString(received, expected) {
+    if (!i18n.isIcuMessage(received)) {
+      const message = () =>
+      [
+        `${this.utils.matcherHint('.toBeDisplayString')}\n`,
+        `Expected object to be an ${this.utils.printExpected('LH.IcuMessage')}`,
+        `Received ${typeof received}`,
+        `  ${this.utils.printReceived(received)}`,
+      ].join('\n');
+
+      return {message, pass: false};
+    }
+
     const actual = i18n.getFormatted(received, 'en-US');
     const pass = expected instanceof RegExp ?
       expected.test(actual) :
@@ -28,7 +40,7 @@ expect.extend({
         `  ${this.utils.printReceived(actual)}`,
       ].join('\n');
 
-    return {actual, message, pass};
+    return {message, pass};
   },
 
   // Expose toBeCloseTo() so it can be used as an asymmetric matcher.