diff --git a/artiq-fast.nix b/artiq-fast.nix
index 5ea4562..3b621cf 100644
--- a/artiq-fast.nix
+++ b/artiq-fast.nix
@@ -60,7 +60,8 @@ in
       name = "extended-tests";
 
       __networked = true;  # compatibility with old patched Nix
-      __impure = true;     # Nix 2.8+
+      # breaks hydra, https://github.com/NixOS/hydra/issues/1216
+      #__impure = true;     # Nix 2.8+
 
       buildInputs = [
         (pkgs.python3.withPackages(ps: [ ps.paramiko artiqpkgs.artiq artiqpkgs.artiq-board-kc705-nist_clock ]))
diff --git a/artiq-zynq.nix b/artiq-zynq.nix
index c778ed3..c8fc6bd 100644
--- a/artiq-zynq.nix
+++ b/artiq-zynq.nix
@@ -22,7 +22,8 @@ in
       name = "zc706-hitl-tests";
 
       __networked = true;  # compatibility with old patched Nix
-      __impure = true;     # Nix 2.8+
+      # breaks hydra, https://github.com/NixOS/hydra/issues/1216
+      #__impure = true;     # Nix 2.8+
 
       buildInputs = [
         pkgs.netcat pkgs.openssh pkgs.rsync artiq-fast.artiq artiq-fast.artiq-netboot