diff --git a/src/app/markdown/markdown.service.spec.ts b/src/app/markdown/markdown.service.spec.ts
index 9d91a51a..d2746c6d 100644
--- a/src/app/markdown/markdown.service.spec.ts
+++ b/src/app/markdown/markdown.service.spec.ts
@@ -168,14 +168,14 @@ describe('MarkdowService', () => {
 
     it('should not call Prism when not available', () => {
 
-      Prism = undefined;
+      global['Prism'] = undefined;
 
       markdownService.highlight();
     });
 
     it('should call Prism when available', () => {
 
-      Prism = { highlightAll: () => {} };
+      global['Prism'] = { highlightAll: () => {} };
 
       spyOn(Prism, 'highlightAll');
 
diff --git a/src/app/markdown/markdown.service.ts b/src/app/markdown/markdown.service.ts
index 9248ea3d..4c3d00fe 100644
--- a/src/app/markdown/markdown.service.ts
+++ b/src/app/markdown/markdown.service.ts
@@ -46,10 +46,9 @@ export class MarkdownService {
   }
 
   highlight() {
-    if (!Prism) {
-      return;
+    if (typeof Prism !== 'undefined') {
+      Prism.highlightAll(false);
     }
-    Prism.highlightAll(false);
   }
 
   private extractData(response: Response) {