diff --git a/public/js/gogs.js b/public/js/gogs.js
index f979df0762b..6c00d27764a 100644
--- a/public/js/gogs.js
+++ b/public/js/gogs.js
@@ -18,6 +18,9 @@ function initCommentPreviewTab($form) {
                 var $preview_tab = $form.find('.tab.segment[data-tab="' + $tab_menu.data('preview') + '"]');
                 $preview_tab.html(data);
                 emojify.run($preview_tab[0]);
+                $('pre code', $preview_tab[0]).each(function(i, block) {
+                    hljs.highlightBlock(block);
+                });
             }
         );
     });
diff --git a/routers/repo/issue.go b/routers/repo/issue.go
index a4efb680248..b031e42ce73 100644
--- a/routers/repo/issue.go
+++ b/routers/repo/issue.go
@@ -291,6 +291,8 @@ func NewIssue(ctx *middleware.Context) {
 		return
 	}
 
+	ctx.Data["RequireHighlightJS"] = true
+
 	ctx.HTML(200, ISSUE_NEW)
 }
 
@@ -623,6 +625,9 @@ func ViewIssue(ctx *middleware.Context) {
 	ctx.Data["Issue"] = issue
 	ctx.Data["IsIssueOwner"] = ctx.Repo.IsAdmin() || (ctx.IsSigned && issue.IsPoster(ctx.User.Id))
 	ctx.Data["SignInLink"] = setting.AppSubUrl + "/user/login"
+
+	ctx.Data["RequireHighlightJS"] = true
+
 	ctx.HTML(200, ISSUE_VIEW)
 }