diff --git a/extension.json b/extension.json
index bdde3b84..26c16d54 100644
--- a/extension.json
+++ b/extension.json
@@ -71,14 +71,6 @@
 			"styles": [
 				"modules/ext.RevisionSlider.less"
 			],
-			"skinStyles": {
-				"monobook": [
-					"modules/ext.RevisionSlider.monobook.css"
-				],
-				"modern": [
-					"modules/ext.RevisionSlider.modern.css"
-				]
-			},
 			"dependencies": [
 				"moment",
 				"oojs-ui",
diff --git a/modules/ext.RevisionSlider.modern.css b/modules/ext.RevisionSlider.modern.css
deleted file mode 100644
index ac5fa8e2..00000000
--- a/modules/ext.RevisionSlider.modern.css
+++ /dev/null
@@ -1,7 +0,0 @@
-/* HACK: Modern uses x-small and a globalWrapper to make everything
-   inside of it appear normal. However, the revslider-tooltips are
-   not inside this globalWrapper, and thus need a separate CSS rule.
-   Once this issue is fixed, this rule can be removed. (T166231) */
-.mw-revslider-tooltip {
-	font-size: 0.8rem;
-}
diff --git a/modules/ext.RevisionSlider.monobook.css b/modules/ext.RevisionSlider.monobook.css
deleted file mode 100644
index b981b163..00000000
--- a/modules/ext.RevisionSlider.monobook.css
+++ /dev/null
@@ -1,7 +0,0 @@
-/* HACK: Monobook uses x-small and a globalWrapper to make everything
-   inside of it appear normal. However, the revslider-tooltips are
-   not inside this globalWrapper, and thus need a separate CSS rule.
-   Once this issue is fixed, this rule can be removed. (T166231) */
-.mw-revslider-tooltip {
-	font-size: 0.8rem;
-}