diff --git a/core/modules/utils/dom/modal.js b/core/modules/utils/dom/modal.js
index b2b3ca2c1..702a5e7b5 100644
--- a/core/modules/utils/dom/modal.js
+++ b/core/modules/utils/dom/modal.js
@@ -50,12 +50,12 @@ Modal.prototype.display = function(title,options) {
 	this.modalCount++;
 	this.adjustPageClass();
 	// Add classes
-	$tw.utils.addClass(wrapper,"modal-wrapper");
-	$tw.utils.addClass(modalBackdrop,"modal-backdrop");
-	$tw.utils.addClass(modalWrapper,"modal");
-	$tw.utils.addClass(modalHeader,"modal-header");
-	$tw.utils.addClass(modalBody,"modal-body");
-	$tw.utils.addClass(modalFooter,"modal-footer");
+	$tw.utils.addClass(wrapper,"tc-modal-wrapper");
+	$tw.utils.addClass(modalBackdrop,"tc-modal-backdrop");
+	$tw.utils.addClass(modalWrapper,"tc-modal");
+	$tw.utils.addClass(modalHeader,"tc-modal-header");
+	$tw.utils.addClass(modalBody,"tc-modal-body");
+	$tw.utils.addClass(modalFooter,"tc-modal-footer");
 	// Join them together
 	wrapper.appendChild(modalBackdrop);
 	wrapper.appendChild(modalWrapper);
diff --git a/themes/tiddlywiki/seamless/base.tid b/themes/tiddlywiki/seamless/base.tid
index 6cc8c9a6c..9726af32d 100644
--- a/themes/tiddlywiki/seamless/base.tid
+++ b/themes/tiddlywiki/seamless/base.tid
@@ -30,12 +30,12 @@ Rules copied from Snow White
 	-webkit-filter: blur(4px);
 }
 
-.modal {
+.tc-modal {
 	border-radius: 6px;
 	<<box-shadow "0 3px 7px rgba(0,0,0,0.3)">>
 }
 
-.modal-footer {
+.tc-modal-footer {
 	border-radius: 0 0 6px 6px;
 	<<box-shadow "inset 0 1px 0 #fff">>;
 }
diff --git a/themes/tiddlywiki/snowwhite/base.tid b/themes/tiddlywiki/snowwhite/base.tid
index 7a64693c7..68ac78fbf 100644
--- a/themes/tiddlywiki/snowwhite/base.tid
+++ b/themes/tiddlywiki/snowwhite/base.tid
@@ -63,12 +63,12 @@ canvas.tw-edit-bitmapeditor  {
 	-webkit-filter: blur(4px);
 }
 
-.modal {
+.tc-modal {
 	border-radius: 6px;
 	<<box-shadow "0 3px 7px rgba(0,0,0,0.3)">>
 }
 
-.modal-footer {
+.tc-modal-footer {
 	border-radius: 0 0 6px 6px;
 	<<box-shadow "inset 0 1px 0 #fff">>;
 }
diff --git a/themes/tiddlywiki/vanilla/base.tid b/themes/tiddlywiki/vanilla/base.tid
index 5081d7230..544b2450c 100644
--- a/themes/tiddlywiki/vanilla/base.tid
+++ b/themes/tiddlywiki/vanilla/base.tid
@@ -973,7 +973,7 @@ canvas.tw-edit-bitmapeditor  {
 ** Modals
 */
 
-.modal-wrapper {
+.tc-modal-wrapper {
 	position: fixed;
 	overflow: auto;
 	overflow-y: scroll;
@@ -983,7 +983,7 @@ canvas.tw-edit-bitmapeditor  {
 	left: 0;
 }
 
-.modal-backdrop {
+.tc-modal-backdrop {
 	position: fixed;
 	top: 0;
 	right: 0;
@@ -993,49 +993,49 @@ canvas.tw-edit-bitmapeditor  {
 	background-color: <<colour modal-backdrop>>;
 }
 
-.modal {
+.tc-modal {
 	z-index: 1100;
 	background-color: <<colour modal-background>>;
 	border: 1px solid <<colour modal-border>>;
 }
 
 @media (max-width: 55em) {
-	.modal {
+	.tc-modal {
 		position: fixed;
 		top: 1em;
 		left: 1em;
 		right: 1em;
 	}
 
-	.modal-body {
+	.tc-modal-body {
 		overflow-y: auto;
 		max-height: 400px;
 	}
 }
 
 @media (min-width: 55em) {
-	.modal {
+	.tc-modal {
 		position: relative;
 		width: 50%;
 		margin: 30px auto;
 	}
 }
 
-.modal-header {
+.tc-modal-header {
 	padding: 9px 15px;
 	border-bottom: 1px solid <<colour modal-header-border>>;
 }
 
-.modal-header h3 {
+.tc-modal-header h3 {
 	margin: 0;
 	line-height: 30px;
 }
 
-.modal-body {
+.tc-modal-body {
 	padding: 15px;
 }
 
-.modal-footer {
+.tc-modal-footer {
 	padding: 14px 15px 15px;
 	margin-bottom: 0;
 	text-align: right;