diff --git a/fieldpattern.cpp b/fieldpattern.cpp
index 324a0ddb..0fe4594a 100644
--- a/fieldpattern.cpp
+++ b/fieldpattern.cpp
@@ -317,7 +317,7 @@ struct fpattern {
 struct discovery {
   fpattern experiment;
   std::shared_ptr<std::thread> discoverer;
-  std::mutex lock, slock;
+  std::recursive_mutex lock, slock;
   bool is_suspended;
   bool stop_it;