diff --git a/.github/workflows/acceptance-test.yml b/.github/workflows/acceptance-test.yml
index 5573daaef68..a6526049e80 100644
--- a/.github/workflows/acceptance-test.yml
+++ b/.github/workflows/acceptance-test.yml
@@ -12,9 +12,10 @@
 # wrong or the architecture is missing from Release, the install fails, which
 # is the point.
 #
-# It runs against a release candidate on the development server, which serves
-# its tree the moment it is written. The download server sits behind an hourly
-# sync to the mirrors, so testing there would mostly measure the sync.
+# It runs against each release candidate on the development server, which
+# serves its tree the moment it is written, and against each published nightly
+# snapshot on ftp.postgresql.org, where snapshot.yml first waits for the hourly
+# sync to the mirrors to deliver everything this test fetches.
 
 name: Acceptance test
 
diff --git a/.github/workflows/snapshot.yml b/.github/workflows/snapshot.yml
index 71a6d33b10b..edf5e288f8c 100644
--- a/.github/workflows/snapshot.yml
+++ b/.github/workflows/snapshot.yml
@@ -463,3 +463,101 @@ jobs:
           else
               publish snapshot-purge
           fi
+
+  # The published snapshot reaches ftp.postgresql.org on the hourly sync from
+  # the download server, not when the publish step finishes, so the acceptance
+  # test cannot simply follow it. This waits until everything that test will
+  # fetch is being served, the signatures and repository indexes included,
+  # since those are written last on the server.
+  #
+  # Each request carries a throwaway query string. The mirrors sit behind
+  # Varnish, and a plain request for a file that has not arrived yet could
+  # leave a cached 404 for exactly the URL the acceptance test asks for next.
+  mirrored:
+    needs: [location, windows, assemble]
+    if: >-
+      always()
+      && needs.assemble.result == 'success'
+      && (github.event_name == 'schedule' || inputs.publish)
+    runs-on: ubuntu-24.04
+    timeout-minutes: 180
+    steps:
+      - name: Wait for the snapshot to reach the mirrors
+        env:
+          BASE_URL: https://ftp.postgresql.org/pub/pgadmin/pgadmin4/snapshots/${{ needs.location.outputs.name }}
+          # The Windows runner is allowed to be offline, in which case the
+          # snapshot has no installer and waiting for one would only time out.
+          # The acceptance test still fails for it, which is right: the run
+          # is already red from the Windows job.
+          WINDOWS: ${{ needs.windows.result }}
+        run: |
+          set -euo pipefail
+
+          # Bounded, so that one stalled connection to a mirror cannot use up
+          # the job's time limit and leave no polls after it.
+          fetch() {
+              curl -fsS --connect-timeout 10 --max-time 60 \
+                  "${BASE_URL}/$1?mirror-check=$(date +%s)"
+          }
+
+          complete() {
+              local listing name
+              listing=$(fetch '') || return 1
+              local wanted=(
+                  'pgadmin4-[0-9.]+\.tar\.gz\.asc'
+                  'pgadmin4-[0-9.]+-py3-none-any\.whl\.asc'
+                  'pgadmin4-[0-9.]+-docs\.tar\.gz\.asc'
+                  'pgadmin4-[0-9.]+\.pdf\.asc'
+                  'pgadmin4-[0-9.]+\.epub\.asc'
+                  'pgadmin4-[0-9.]+-arm64\.dmg'
+                  'pgadmin4-[0-9.]+-x64\.dmg'
+              )
+              [ "${WINDOWS}" = "success" ] && wanted+=('pgadmin4-[0-9.]+-x64\.exe')
+              for name in "${wanted[@]}"; do
+                  grep -Eq "\"${name}\"" <<< "${listing}" || {
+                      echo "  not yet: ${name}"; return 1; }
+              done
+
+              for name in bookworm trixie jammy noble resolute; do
+                  fetch "apt/${name}/dists/pgadmin4/InRelease" >/dev/null || {
+                      echo "  not yet: apt/${name}"; return 1; }
+              done
+              for name in redhat/rhel-9 redhat/rhel-10 fedora/fedora-43 fedora/fedora-44; do
+                  fetch "yum/${name}-x86_64/repodata/repomd.xml.asc" >/dev/null || {
+                      echo "  not yet: yum/${name}"; return 1; }
+              done
+          }
+
+          # Up to two and a half hours: two sync intervals and some slack. The
+          # limit is on elapsed time rather than on attempts, since a check can
+          # make ten requests of up to a minute each against a stalled mirror,
+          # and counting attempts would then run into the job's own timeout.
+          deadline=$((SECONDS + 150 * 60))
+          attempt=0
+          while :; do
+              attempt=$((attempt + 1))
+              echo "Check ${attempt} of ${BASE_URL}"
+              if complete; then
+                  echo "The snapshot is being served."
+                  exit 0
+              fi
+              [ "${SECONDS}" -lt "${deadline}" ] || break
+              # The last wait is cut short, so that a final check still runs
+              # at the deadline rather than being skipped.
+              wait=$((deadline - SECONDS))
+              if [ "${wait}" -gt 300 ]; then
+                  wait=300
+              fi
+              sleep "${wait}"
+          done
+          echo "The snapshot had not reached the mirrors after 150 minutes." >&2
+          exit 1
+
+  # Installing from the published snapshot, as the release candidate does,
+  # so that a defect only visible in what a user downloads shows up the next
+  # morning rather than when a release is being cut.
+  acceptance:
+    needs: [location, mirrored]
+    uses: ./.github/workflows/acceptance-test.yml
+    with:
+      base-url: https://ftp.postgresql.org/pub/pgadmin/pgadmin4/snapshots/${{ needs.location.outputs.name }}