diff --git a/src/utils.ts b/src/utils.ts
index b0514c3..33845cc 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -71,7 +71,7 @@ export function splitAndPrefix(
         }
       }
 
-      if (keep) {
+      if (keep && foundPrefix) {
         foundPrefix = foundPrefix.replace(new RegExp(`[^${keep.join('')}]`, 'g'), '')
       }