diff --git a/bind9.18.spec b/bind9.18.spec
index 615a480..1d59b0e 100644
--- a/bind9.18.spec
+++ b/bind9.18.spec
@@ -505,6 +505,7 @@ export TSAN_OPTIONS="log_exe_name=true log_path=ThreadSanitizer exitcode=0"
     THREADS=16
     ulimit -n 8092 || : # Requires on some machines with many cores
   fi
+  export ISC_TASK_WORKERS="$THREADS"
   e=0
   make unit -j${THREADS} || e=$?
   # Display details of failure