diff --git a/app/src/main/java/io/legado/app/utils/UrlUtil.kt b/app/src/main/java/io/legado/app/utils/UrlUtil.kt
index 0b096e055..15c01d034 100644
--- a/app/src/main/java/io/legado/app/utils/UrlUtil.kt
+++ b/app/src/main/java/io/legado/app/utils/UrlUtil.kt
@@ -93,12 +93,12 @@ object UrlUtil {
     }
 
     /* 获取合法的文件后缀 */
-    fun getSuffix(url: String, default: String? = null): String {
-        val suffix = url.substringAfterLast(".").substringBeforeLast(",")
+    fun getSuffix(str: String, default: String? = null): String {
+        val suffix = str.substringAfterLast(".").substringBeforeLast(",")
         //检查截取的后缀字符是否合法 [a-zA-Z0-9]
         val fileSuffixRegex = Regex("^[a-z\\d]+$", RegexOption.IGNORE_CASE)
         return if (suffix.length > 5 || !suffix.matches(fileSuffixRegex)) {
-            default ?: throw IllegalArgumentException("Cannot find illegal suffix")
+            default ?: throw IllegalArgumentException("Cannot find illegal suffix:\n target: $str\nsuffix: $suffix")
         } else {
             suffix
         }