diff --git a/app/src/main/java/com/hippo/yorozuya/IOUtils.kt b/app/src/main/java/com/hippo/yorozuya/IOUtils.kt
index 10c89385a..5a6561189 100644
--- a/app/src/main/java/com/hippo/yorozuya/IOUtils.kt
+++ b/app/src/main/java/com/hippo/yorozuya/IOUtils.kt
@@ -4,11 +4,13 @@ import okhttp3.ResponseBody
 import java.io.File
 
 fun ResponseBody.copyToFile(file: File) {
+    val length = contentLength()
+    check(length > 0) { "contentLength < 0!" }
     val os = file.outputStream()
     val channel = os.channel
     val source = source()
     try {
-        channel.transferFrom(source, 0, contentLength())
+        channel.transferFrom(source, 0, length)
     } catch (e: Throwable) {
         throw e
     } finally {