diff --git a/src/libstore/build/local-derivation-goal.cc b/src/libstore/build/local-derivation-goal.cc
index cfcda1311..8837ac25d 100644
--- a/src/libstore/build/local-derivation-goal.cc
+++ b/src/libstore/build/local-derivation-goal.cc
@@ -530,7 +530,9 @@ void LocalDerivationGoal::startBuilder()
         /* Schedule this scratch output path for automatic deletion
          * if we do not cancel it, e.g. when registering the outputs.
          */
-        scratchOutputsCleaner.insert_or_assign(outputName, worker.store.printStorePath(scratchPath));
+        scratchOutputsCleaner.emplace(
+            outputName, worker.store.toRealPath(worker.store.printStorePath(scratchPath))
+        );
 
         /* Substitute output placeholders with the scratch output paths.
            We'll use during the build. */