diff --git a/typo3/sysext/backend/Resources/Public/JavaScript/AjaxDataHandler.js b/typo3/sysext/backend/Resources/Public/JavaScript/AjaxDataHandler.js
index 71479ae143561f82a57c48a05daaef8cdc3102c1..ae4a8617db79a81b8f19fc7745c01412e6b84b37 100644
--- a/typo3/sysext/backend/Resources/Public/JavaScript/AjaxDataHandler.js
+++ b/typo3/sysext/backend/Resources/Public/JavaScript/AjaxDataHandler.js
@@ -70,6 +70,7 @@ define(['jquery', 'TYPO3/CMS/Backend/Modal', 'TYPO3/CMS/Backend/Notification'],
 				{
 					text: $(this).data('button-close-text') || TYPO3.lang['button.cancel'] || 'Cancel',
 					active: true,
+					btnClass: 'btn-default',
 					name: 'cancel'
 				},
 				{
diff --git a/typo3/sysext/backend/Resources/Public/JavaScript/DragUploader.js b/typo3/sysext/backend/Resources/Public/JavaScript/DragUploader.js
index 24de4bca0d9b9d7bc029266b06bc2289d78918cd..c08d710b3e20113f16c18661e9d6f66626967d28 100644
--- a/typo3/sysext/backend/Resources/Public/JavaScript/DragUploader.js
+++ b/typo3/sysext/backend/Resources/Public/JavaScript/DragUploader.js
@@ -288,6 +288,7 @@ define(['jquery', 'moment', 'nprogress', 'TYPO3/CMS/Backend/Modal', 'TYPO3/CMS/L
 				{
 					text: $(this).data('button-close-text') || TYPO3.lang['file_upload.button.cancel'] || 'Cancel',
 					active: true,
+					btnClass: 'btn-default',
 					name: 'cancel'
 				},
 				{
diff --git a/typo3/sysext/backend/Resources/Public/JavaScript/FormEngine.js b/typo3/sysext/backend/Resources/Public/JavaScript/FormEngine.js
index 47cc40ce9a48c2b7c47b07da06b4f5d09c2ca6bd..49754c23be56fa8cada5949865126195878c1f5b 100644
--- a/typo3/sysext/backend/Resources/Public/JavaScript/FormEngine.js
+++ b/typo3/sysext/backend/Resources/Public/JavaScript/FormEngine.js
@@ -601,6 +601,7 @@ define(['jquery', 'TYPO3/CMS/Backend/Modal'], function ($, Modal) {
 				{
 					text: TYPO3.lang['buttons.confirm.delete_record.no'] || 'Cancel',
 					active: true,
+					btnClass: 'btn-default',
 					name: 'no'
 				},
 				{
@@ -628,6 +629,7 @@ define(['jquery', 'TYPO3/CMS/Backend/Modal'], function ($, Modal) {
 				{
 					text: TYPO3.lang['buttons.confirm.delete_record.no'] || 'Cancel',
 					active: true,
+					btnClass: 'btn-default',
 					name: 'no'
 				},
 				{
@@ -837,10 +839,11 @@ define(['jquery', 'TYPO3/CMS/Backend/Modal'], function ($, Modal) {
 		if ($('.has-change').length > 0) {
 			var title = TYPO3.lang['label.confirm.close_without_save.title'] || 'Do you want to quit without saving?';
 			var content = TYPO3.lang['label.confirm.close_without_save.content'] || 'You have currently unsaved changes. Are you sure that you want to discard all changes?';
-			$modal = Modal.confirm(title, content, top.TYPO3.Severity.warning, [
+			var $modal = Modal.confirm(title, content, top.TYPO3.Severity.warning, [
 				{
 					text: TYPO3.lang['buttons.confirm.close_without_save.no'] || 'No, I will continue editing',
 					active: true,
+					btnClass: 'btn-default',
 					name: 'no'
 				},
 				{
diff --git a/typo3/sysext/backend/Resources/Public/JavaScript/Modal.js b/typo3/sysext/backend/Resources/Public/JavaScript/Modal.js
index c72c9d5916450a8277b04c4a16f1f5e5d49d0c31..dce9d83f5b8bf367a22cf06d6be0a45f28962ba0 100644
--- a/typo3/sysext/backend/Resources/Public/JavaScript/Modal.js
+++ b/typo3/sysext/backend/Resources/Public/JavaScript/Modal.js
@@ -104,6 +104,7 @@ define(['jquery', 'TYPO3/CMS/Backend/Notification', 'bootstrap'], function($) {
 				{
 					text: $(this).data('button-close-text') || TYPO3.lang['button.cancel'] || 'Cancel',
 					active: true,
+					btnClass: 'btn-default',
 					name: 'cancel'
 				},
 				{
diff --git a/typo3/sysext/extensionmanager/Resources/Public/JavaScript/Main.js b/typo3/sysext/extensionmanager/Resources/Public/JavaScript/Main.js
index cbc84f5da0794bb23208881e3a259477df834b1d..a4f652b7486931f46caeba97ec7b22e3b3f59504 100644
--- a/typo3/sysext/extensionmanager/Resources/Public/JavaScript/Main.js
+++ b/typo3/sysext/extensionmanager/Resources/Public/JavaScript/Main.js
@@ -81,6 +81,7 @@ define(['jquery', 'nprogress', 'TYPO3/CMS/Backend/Modal', 'datatables', 'TYPO3/C
 						{
 							text: TYPO3.lang['button.cancel'],
 							active: true,
+							btnClass: 'btn-default',
 							trigger: function() {
 								Modal.dismiss();
 							}
@@ -197,6 +198,7 @@ define(['jquery', 'nprogress', 'TYPO3/CMS/Backend/Modal', 'datatables', 'TYPO3/C
 				{
 					text: TYPO3.lang['button.cancel'],
 					active: true,
+					btnClass: 'btn-default',
 					trigger: function() {
 						Modal.dismiss();
 					}
@@ -386,6 +388,7 @@ define(['jquery', 'nprogress', 'TYPO3/CMS/Backend/Modal', 'datatables', 'TYPO3/C
 				{
 					text: TYPO3.lang['button.cancel'],
 					active: true,
+					btnClass: 'btn-default',
 					trigger: function() {
 						Modal.dismiss();
 					}
@@ -423,6 +426,7 @@ define(['jquery', 'nprogress', 'TYPO3/CMS/Backend/Modal', 'datatables', 'TYPO3/C
 						{
 							text: TYPO3.lang['button.cancel'],
 							active: true,
+							btnClass: 'btn-default',
 							trigger: function() {
 								Modal.dismiss();
 							}
diff --git a/typo3/sysext/recycler/Resources/Public/JavaScript/Recycler.js b/typo3/sysext/recycler/Resources/Public/JavaScript/Recycler.js
index f72cefe5d134b79878dd5072500822e8b474aad4..90a2cf34ea45c4858873e6bc3cbf56db8d92a0aa 100644
--- a/typo3/sysext/recycler/Resources/Public/JavaScript/Recycler.js
+++ b/typo3/sysext/recycler/Resources/Public/JavaScript/Recycler.js
@@ -349,6 +349,7 @@ define(['jquery', 'nprogress', 'TYPO3/CMS/Backend/Modal', 'TYPO3/CMS/Backend/jqu
 		Modal.confirm(TYPO3.lang['modal.delete.header'], message, top.TYPO3.Severity.error, [
 			{
 				text: TYPO3.lang['button.cancel'],
+				btnClass: 'btn-default',
 				trigger: function() {
 					Modal.dismiss();
 				}
@@ -397,6 +398,7 @@ define(['jquery', 'nprogress', 'TYPO3/CMS/Backend/Modal', 'TYPO3/CMS/Backend/jqu
 		Modal.confirm(TYPO3.lang['modal.undo.header'], $message, top.TYPO3.Severity.ok, [
 			{
 				text: TYPO3.lang['button.cancel'],
+				btnClass: 'btn-default',
 				trigger: function() {
 					Modal.dismiss();
 				}