diff --git a/src/libstore/build/derivation-building-goal.cc b/src/libstore/build/derivation-building-goal.cc
index fd85a066d..510304653 100644
--- a/src/libstore/build/derivation-building-goal.cc
+++ b/src/libstore/build/derivation-building-goal.cc
@@ -602,12 +602,11 @@ Goal::Co DerivationBuildingGoal::tryToBuild()
 #ifdef _WIN32 // TODO enable `DerivationBuilder` on Windows
     throw UnimplementedError("building derivations is not yet implemented on Windows");
 #else
+    assert(!hook);
 
     // Will continue here while waiting for a build user below
     while (true) {
 
-        assert(!hook);
-
         unsigned int curBuilds = worker.getNrLocalBuilds();
         if (curBuilds >= settings.maxBuildJobs) {
             outputLocks.unlock();