diff --git a/src/schema.ts b/src/schema.ts
index 23e2938d..6147f562 100644
--- a/src/schema.ts
+++ b/src/schema.ts
@@ -66,7 +66,9 @@ const localeSchema = z.string().transform<Intl.Locale>((val, ctx) => {
 });
 
 /** White-space separated list of sizes, each in the format <number with up to 4 digits>x<number with up to 4 digits> or with "X" in upper case. */
-const sizesSchema = z.string().regex(/^(?:[1-9]\d{0,3}[xX][1-9]\d{0,3})(?:\s+[1-9]\d{0,3}[xX][1-9]\d{0,3})*$/);
+const sizesSchema = z.string().refine((value) =>
+  value.split(' ').every((v) => /^[1-9]\d{0,3}[xX][1-9]\d{0,3}$/.test(v))
+);
 
 export {
   booleanParamSchema,