diff --git a/packages/svelte/src/compiler/phases/2-analyze/css/css-prune.js b/packages/svelte/src/compiler/phases/2-analyze/css/css-prune.js
index d5e0e82724..ca7476ef7f 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/css/css-prune.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/css/css-prune.js
@@ -784,7 +784,7 @@ function attribute_matches(node, name, expected_value, operator, case_insensitiv
 					prev_values.push(current_possible_value);
 				}
 			});
-			if (prev_values.length < current_possible_values.size) {
+			if (prev_values.length < current_possible_values.length) {
 				prev_values.push(' ');
 			}
 			if (prev_values.length > 20) {
diff --git a/packages/svelte/src/compiler/phases/2-analyze/css/utils.js b/packages/svelte/src/compiler/phases/2-analyze/css/utils.js
index 5acd71a7bf..45ba06e55e 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/css/utils.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/css/utils.js
@@ -80,7 +80,7 @@ function gather_possible_values(node, is_class, set, is_nested = false) {
 /**
  * @param {AST.Text | AST.ExpressionTag} chunk
  * @param {boolean} is_class
- * @returns {Set<string | number | boolean> | null}
+ * @returns {string[] | null}
  */
 export function get_possible_values(chunk, is_class) {
 	const values = new Set();
@@ -92,7 +92,7 @@ export function get_possible_values(chunk, is_class) {
 	}
 
 	if (values.has(UNKNOWN)) return null;
-	return values;
+	return [...values].map((value) => String(value));
 }
 
 /**