diff --git a/polygerrit-ui/app/elements/diff/gr-syntax-lib-loader/gr-syntax-lib-loader.js b/polygerrit-ui/app/elements/diff/gr-syntax-lib-loader/gr-syntax-lib-loader.js
index bfd8e90b1c..ca3cf62293 100644
--- a/polygerrit-ui/app/elements/diff/gr-syntax-lib-loader/gr-syntax-lib-loader.js
+++ b/polygerrit-ui/app/elements/diff/gr-syntax-lib-loader/gr-syntax-lib-loader.js
@@ -26,6 +26,7 @@
 
         // NOTE: intended singleton.
         value: {
+          configured: false,
           loading: false,
           callbacks: [],
         },
@@ -60,12 +61,13 @@
     },
 
     _getHighlightLib() {
-      return window.hljs;
-    },
+      const lib = window.hljs;
+      if (lib && !this._state.configured) {
+        this._state.configured = true;
 
-    _configureHighlightLib() {
-      this._getHighlightLib().configure(
-          {classPrefix: 'gr-diff gr-syntax gr-syntax-'});
+        lib.configure({classPrefix: 'gr-diff gr-syntax gr-syntax-'});
+      }
+      return lib;
     },
 
     _getLibRoot() {
@@ -93,10 +95,8 @@
         }
 
         script.src = src;
-        script.onload = function() {
-          this._configureHighlightLib();
-          resolve();
-        }.bind(this);
+        script.onload = resolve;
+        script.onerror = reject;
         Polymer.dom(document.head).appendChild(script);
       });
     },
diff --git a/polygerrit-ui/app/elements/diff/gr-syntax-lib-loader/gr-syntax-lib-loader_test.html b/polygerrit-ui/app/elements/diff/gr-syntax-lib-loader/gr-syntax-lib-loader_test.html
index 6ddde4698d..6e88ed1d38 100644
--- a/polygerrit-ui/app/elements/diff/gr-syntax-lib-loader/gr-syntax-lib-loader_test.html
+++ b/polygerrit-ui/app/elements/diff/gr-syntax-lib-loader/gr-syntax-lib-loader_test.html
@@ -55,6 +55,7 @@ limitations under the License.
       loadStub.restore();
 
       // Because the element state is a singleton, clean it up.
+      element._state.configured = false;
       element._state.loading = false;
       element._state.callbacks = [];
     });
@@ -88,8 +89,13 @@ limitations under the License.
     });
 
     suite('preloaded', () => {
+      let hljsStub;
+
       setup(() => {
-        window.hljs = 'test-object';
+        hljsStub = {
+          configure: sinon.stub(),
+        };
+        window.hljs = hljsStub;
       });
 
       teardown(() => {
@@ -101,7 +107,14 @@ limitations under the License.
         element.get().then(firstCallHandler);
         flush(() => {
           assert.isTrue(firstCallHandler.called);
-          assert.isTrue(firstCallHandler.calledWith('test-object'));
+          assert.isTrue(firstCallHandler.calledWith(hljsStub));
+          done();
+        });
+      });
+
+      test('configures hljs', done => {
+        element.get().then(() => {
+          assert.isTrue(window.hljs.configure.calledOnce);
           done();
         });
       });