diff --git a/nix/libstore/build.cc b/nix/libstore/build.cc
index 8d3b216265..17085ad3f7 100644
--- a/nix/libstore/build.cc
+++ b/nix/libstore/build.cc
@@ -2336,7 +2336,7 @@ void DerivationGoal::registerOutputs()
         if (buildMode == bmCheck) {
             ValidPathInfo info = worker.store.queryPathInfo(path);
             if (hash.first != info.hash)
-                throw Error(format("derivation `%2%' may not be deterministic: hash mismatch in output `%1%'") % drvPath % path);
+                throw Error(format("derivation `%1%' may not be deterministic: hash mismatch in output `%2%'") % drvPath % path);
             continue;
         }