diff --git a/src/compiler/compile/css/Selector.ts b/src/compiler/compile/css/Selector.ts
index 8569ef8b64..42a60c15f7 100644
--- a/src/compiler/compile/css/Selector.ts
+++ b/src/compiler/compile/css/Selector.ts
@@ -42,7 +42,7 @@ export default class Selector {
 		this.blocks = group_selectors(node);
 
 		// take trailing :global(...) selectors out of consideration
-		const i = this.blocks.findIndex(block => !block.global);
+		const i = this.blocks.findLastIndex(block => !block.global);
 
 		this.local_blocks = this.blocks.slice(0, i);
 
diff --git a/src/compiler/interfaces.ts b/src/compiler/interfaces.ts
index 248175da59..276c9f6abf 100644
--- a/src/compiler/interfaces.ts
+++ b/src/compiler/interfaces.ts
@@ -1,6 +1,15 @@
 import { AssignmentExpression, Node, Program } from 'estree';
 import { SourceMap } from 'magic-string';
 
+declare global {
+  interface Array<T> {
+    findLastIndex(
+      predicate: (value: T, index: number, obj: T[]) => unknown,
+      thisArg?: any
+    ): number
+  }
+}
+
 interface BaseNode {
 	start: number;
 	end: number;