diff --git a/nix/modules/hive-ci.nix b/nix/modules/hive-ci.nix
index a4168136..a8f0012c 100644
--- a/nix/modules/hive-ci.nix
+++ b/nix/modules/hive-ci.nix
@@ -393,6 +393,13 @@ in
           # sandboxing always fails. Fall back to unsandboxed builds.
           # See docs/gotchas.md.
           nix.settings.sandbox-fallback = lib.mkForce true;
+          # Build locally when a configured remote builder is unreachable
+          # instead of hard-failing. Without this a single down/unresolvable
+          # build machine (e.g. a DNS blip on a `nix.buildMachines` host)
+          # turns every cache-miss `nix flake check` red hive-wide — CI must
+          # degrade to a slower local build, not fail. (`sandbox-fallback`
+          # above is unrelated: it only governs the sandbox, not builders.)
+          nix.settings.fallback = lib.mkForce true;
           nix.settings.experimental-features = [
             "nix-command"
             "flakes"