diff --git a/third_party/nix/src/proto/worker.proto b/third_party/nix/src/proto/worker.proto
index d018fe247..d3e8f65f2 100644
--- a/third_party/nix/src/proto/worker.proto
+++ b/third_party/nix/src/proto/worker.proto
@@ -74,6 +74,10 @@ service Worker {
 
   // Query which of the given paths have substitutes.
   rpc QuerySubstitutablePaths(StorePaths) returns (StorePaths);
+
+  // Return all currently valid derivations that have the given store path as an
+  // output.
+  rpc QueryValidDerivers(StorePath) returns (StorePaths);
 }
 
 enum HashType {