diff --git a/.github/workflows/bwrap.yml b/.github/workflows/bwrap.yml
index eab6bc4f..6aa3c01b 100644
--- a/.github/workflows/bwrap.yml
+++ b/.github/workflows/bwrap.yml
@@ -14,7 +14,7 @@ on:
 jobs:
   pass1:
     name: Run up to Linux build under bubblewrap
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-24.04
     steps:
       - name: Install bubblewrap
         run: sudo apt install bubblewrap
@@ -63,7 +63,7 @@ jobs:
   pass2:
     name: Run up to Python bootstrap under bubblewrap
     needs: pass1
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-24.04
     steps:
       - name: Install bubblewrap
         run: sudo apt install bubblewrap
@@ -118,7 +118,7 @@ jobs:
   pass3:
     name: Run remaining builds under bubblewrap
     needs: pass2
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-24.04
     steps:
       - name: Install bubblewrap
         run: sudo apt install bubblewrap
diff --git a/steps/flex-2.5.11/sources b/steps/flex-2.5.11/sources
index 19dd8799..7d7de24f 100644
--- a/steps/flex-2.5.11/sources
+++ b/steps/flex-2.5.11/sources
@@ -1 +1 @@
-http://download.nust.na/pub2/openpkg1/sources/DST/flex/flex-2.5.11.tar.gz bc79b890f35ca38d66ff89a6e3758226131e51ccbd10ef78d5ff150b7bd73689
+http://ftp-tel.sjtu.edu.cn/sites/ftp.openpkg.org/sources/DST/flex/flex-2.5.11.tar.gz bc79b890f35ca38d66ff89a6e3758226131e51ccbd10ef78d5ff150b7bd73689
diff --git a/steps/flex-2.5.33/sources b/steps/flex-2.5.33/sources
index 226c7204..8acd3235 100644
--- a/steps/flex-2.5.33/sources
+++ b/steps/flex-2.5.33/sources
@@ -1 +1 @@
-http://download.nust.na/pub2/openpkg1/sources/DST/flex/flex-2.5.33.tar.gz c40385e142989c91989413f3c5a31282b2ffdca16b69cd3ecfde537b8a474921
+http://ftp-tel.sjtu.edu.cn/sites/ftp.openpkg.org/sources/DST/flex/flex-2.5.33.tar.gz c40385e142989c91989413f3c5a31282b2ffdca16b69cd3ecfde537b8a474921