diff --git a/Jenkinsfile.backend-docker b/Jenkinsfile.backend-docker
index f130caa..c06f3da 100644
--- a/Jenkinsfile.backend-docker
+++ b/Jenkinsfile.backend-docker
@@ -79,7 +79,9 @@ pipeline {
                     test -f admin-web/package-lock.json
                     mkdir -p artifacts
                     available_kb=$(df -Pk "$WORKSPACE" | awk 'NR == 2 { print $4 }')
-                    test "$available_kb" -ge 8388608
+                    # Warm Docker layers consume disk but make incremental builds
+                    # much smaller; keep 4 GiB free for image export and smoke tests.
+                    test "$available_kb" -ge 4194304
                 '''
             }
         }