diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 2eb654c..de161ba 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -34,12 +34,17 @@ jobs:
           wget -O dl/${IB_NAME}.tar.xz ${IB_URL}${IB_NAME}.tar.xz
           wget -O dl/${MF_NAME} ${IB_URL}${MF_NAME}
           wget -O dl/sha256sums ${IB_URL}sha256sums
+          [ -s dl/sha256sums ]
+          [ -s dl/${MF_NAME} ]
+          [ -s dl/${IB_NAME}.tar.xz ]
+          grep -Fq ${MF_NAME} dl/sha256sums
+          grep -Fq ${IB_NAME}.tar.xz dl/sha256sums
           cd dl && sha256sum -c --ignore-missing --status sha256sums
 
       - name: Unpack IB
         run: |
           mkdir ib
-          tar -C ib --strip-components=1 -xJf ../dl/${IB_NAME}.tar.xz
+          tar -C ib --strip-components=1 -xJf dl/${IB_NAME}.tar.xz
           cp -a src/* ib/
           ls patches/ | sort | xargs -n1 sh -c 'patch -p1 -d ib -i ../patches/$0'
           sed -i 's/ unofficial/ oversea/' ib/Makefile