diff --git a/flake.nix b/flake.nix
index d954bd29d..be966f498 100644
--- a/flake.nix
+++ b/flake.nix
@@ -13,7 +13,7 @@
       versionSuffix =
         if officialRelease
         then ""
-        else "pre${builtins.substring 0 8 self.lastModifiedDate}_${self.shortRev or "dirty"}";
+        else "pre${builtins.substring 0 8 (self.lastModifiedDate or self.lastModified)}_${self.shortRev or "dirty"}";
 
       officialRelease = false;