diff --git a/src/lib/Hydra/Controller/Build.pm b/src/lib/Hydra/Controller/Build.pm
index 7e69b79b..5c62b0ad 100644
--- a/src/lib/Hydra/Controller/Build.pm
+++ b/src/lib/Hydra/Controller/Build.pm
@@ -360,9 +360,13 @@ sub restart : Chained('build') PathPart Args(0) {
     requireProjectOwner($c, $build->project);
 
     txn_do($c->model('DB')->schema, sub {
+        my $drvpath = $build->drvpath ;
         error($c, "This build cannot be restarted.")
-            unless $build->finished;
+            unless $build->finished && -f $drvpath ;
 
+        my $cmd = "`nix-store -qR $drvpath`";
+        my $r = `nix-store --clear-failed-paths $cmd`;
+  
         $build->update({finished => 0, timestamp => time});
 
         $build->resultInfo->delete;