diff --git a/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/network/protocol/packet/login/WtLogin.kt b/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/network/protocol/packet/login/WtLogin.kt
index 3ad8f07ed..6c7c5b26b 100644
--- a/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/network/protocol/packet/login/WtLogin.kt
+++ b/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/network/protocol/packet/login/WtLogin.kt
@@ -385,7 +385,7 @@ internal class WtLogin {
 
 
                 val buffer = IoBuffer.Pool.borrow()
-                imageData.readFully(buffer)
+                imageData.readAvailable(buffer)
                 return LoginPacketResponse.Captcha.Picture(
                     data = buffer,
                     sign = sign