diff --git a/nixbld-etc-nixos/configuration.nix b/nixbld-etc-nixos/configuration.nix
index 4d0d6d2..fbfc0dd 100644
--- a/nixbld-etc-nixos/configuration.nix
+++ b/nixbld-etc-nixos/configuration.nix
@@ -468,6 +468,7 @@ in
       patches = oa.patches or [] ++ [
         ./hydra-conda.patch
         ./hydra-restrictdist.patch
+        ./hydra-hack-allowed-uris.patch  # work around https://github.com/NixOS/nix/issues/5039
       ];
       hydraPath = oa.hydraPath + ":" + super.lib.makeBinPath [ super.jq ];
     });
diff --git a/nixbld-etc-nixos/hydra-hack-allowed-uris.patch b/nixbld-etc-nixos/hydra-hack-allowed-uris.patch
new file mode 100644
index 0000000..ed15d92
--- /dev/null
+++ b/nixbld-etc-nixos/hydra-hack-allowed-uris.patch
@@ -0,0 +1,13 @@
+diff --git a/src/hydra-eval-jobs/hydra-eval-jobs.cc b/src/hydra-eval-jobs/hydra-eval-jobs.cc
+index 934bf42e..48f2d248 100644
+--- a/src/hydra-eval-jobs/hydra-eval-jobs.cc
++++ b/src/hydra-eval-jobs/hydra-eval-jobs.cc
+@@ -281,6 +281,8 @@ int main(int argc, char * * argv)
+            to the environment. */
+         evalSettings.restrictEval = true;
+ 
++        evalSettings.allowedUris = {"https://github.com/m-labs/misoc.git"};
++
+         /* When building a flake, use pure evaluation (no access to
+            'getEnv', 'currentSystem' etc. */
+         evalSettings.pureEval = myArgs.flake;