diff --git a/deploy/nixos/configuration.nix b/deploy/nixos/configuration.nix
index 9ea2f21..d473a42 100644
--- a/deploy/nixos/configuration.nix
+++ b/deploy/nixos/configuration.nix
@@ -199,11 +199,18 @@
       auto-optimise-store = true;
     };
 
-    # Garbage collection
+    # Garbage collection — daily at 03:30, 30 min before the 04:00 auto-
+    # upgrade so each upgrade attempt gets the freshest headroom. 15GB
+    # eMMC + ~7GB closure means cross-release upgrades are always tight;
+    # weekly was leaving up to a week of generations stacked when the
+    # upgrade ran (caught 2026-05-26 on the 24.05 → 24.11 attempt).
+    # persistent so a Sintra that was powered off at 03:30 still runs the
+    # GC on next boot rather than skipping until next week.
     gc = {
       automatic = true;
-      dates = "weekly";
+      dates = "03:30";
       options = "--delete-older-than 7d";
+      persistent = true;
     };
   };
 }