Guard a forward declaration.

diff --git a/include/deal.II/base/multithread_info.h b/include/deal.II/base/multithread_info.h
index 34a74d0892230161b8d4c85bf7fee484e0208016..c0370ac57b7daf1360bef4b9e3a8a45f95e13060 100644 (file)
--- a/include/deal.II/base/multithread_info.h
+++ b/include/deal.II/base/multithread_info.h
@@ -25,11 +25,14 @@
 
 #  include <memory>
 
+#  ifdef DEAL_II_WITH_TASKFLOW
 // forward declaration from <taskflow/taskflow.hpp>
 namespace tf
 {
   class Executor;
 }
+#  endif
+
 
 DEAL_II_NAMESPACE_OPEN