diff --git a/src/test/unit_test/SuiteJournal.h b/src/test/unit_test/SuiteJournal.h
index b5c59f3d29..d56c297b0a 100644
--- a/src/test/unit_test/SuiteJournal.h
+++ b/src/test/unit_test/SuiteJournal.h
@@ -94,6 +94,8 @@ SuiteJournalSink::writeAlways(
         return "FTL:";
     }();
 
+    static std::mutex log_mutex;
+    std::lock_guard lock(log_mutex);
     suite_.log << s << partition_ << text << std::endl;
 }