diff --git a/src/libstore/unix/build/derivation-builder.cc b/src/libstore/unix/build/derivation-builder.cc
index b089a0169..fd62aa664 100644
--- a/src/libstore/unix/build/derivation-builder.cc
+++ b/src/libstore/unix/build/derivation-builder.cc
@@ -922,7 +922,7 @@ DerivationBuilderImpl::PathsInChroot DerivationBuilderImpl::getPathsInSandbox()
                 store.computeFSClosure(store.toStorePath(i.second.source).first, closure);
         } catch (InvalidPath & e) {
         } catch (Error & e) {
-            e.addTrace({}, "while processing 'sandbox-paths'");
+            e.addTrace({}, "while processing sandbox path '%s'", i.second.source);
             throw;
         }
     for (auto & i : closure) {
diff --git a/tests/functional/repl.sh b/tests/functional/repl.sh
index 6db9e2d3d..bfe18c9e5 100755
--- a/tests/functional/repl.sh
+++ b/tests/functional/repl.sh
@@ -67,7 +67,7 @@ testRepl () {
 # Simple test, try building a drv
 testRepl
 # Same thing (kind-of), but with a remote store.
-testRepl --store "$TEST_ROOT/store?real=$NIX_STORE_DIR"
+testRepl --store "$TEST_ROOT/other-root?real=$NIX_STORE_DIR"
 
 # Remove ANSI escape sequences. They can prevent grep from finding a match.
 stripColors () {