diff --git a/src/libstore/worker-protocol.hh b/src/libstore/worker-protocol.hh
index 3fdfa1807..56d03af55 100644
--- a/src/libstore/worker-protocol.hh
+++ b/src/libstore/worker-protocol.hh
@@ -10,9 +10,9 @@ namespace nix {
 
 
 typedef enum {
-    wopQuit,
+    wopQuit = 0,
     wopIsValidPath,
-    wopHasSubstitutes,
+    wopHasSubstitutes = 3,
     wopQueryPathHash,
     wopQueryReferences,
     wopQueryReferrers,