diff --git a/src/libstore/build/derivation-goal.cc b/src/libstore/build/derivation-goal.cc
index 97ba994ad..46399b0a8 100644
--- a/src/libstore/build/derivation-goal.cc
+++ b/src/libstore/build/derivation-goal.cc
@@ -1553,11 +1553,12 @@ void DerivationGoal::waiteeDone(GoalPtr waitee, ExitCode result)
     Goal::waiteeDone(waitee, result);
 
     if (!useDerivation) return;
-    auto & fullDrv = *dynamic_cast<Derivation *>(drv.get());
 
     auto * dg = dynamic_cast<DerivationGoal *>(&*waitee);
     if (!dg) return;
 
+    auto & fullDrv = *dynamic_cast<Derivation *>(drv.get());
+
     auto * nodeP = fullDrv.inputDrvs.findSlot(DerivedPath::Opaque { .path = dg->drvPath });
     if (!nodeP) return;
     auto & outputs = nodeP->value;