diff --git a/nestkernel/per_thread_bool_indicator.cpp b/nestkernel/per_thread_bool_indicator.cpp
index 105b7ca2c6..267f753298 100644
--- a/nestkernel/per_thread_bool_indicator.cpp
+++ b/nestkernel/per_thread_bool_indicator.cpp
@@ -67,6 +67,8 @@ PerThreadBoolIndicator::all_false() const
 // We need two barriers here to ensure that no thread can continue and change the result
 // before all threads have determined the result.
 #pragma omp barrier
+  // We need two barriers here to ensure that no thread can continue and change the result
+  // before all threads have determined the result.
   bool ret = ( are_true_ == 0 );
 #pragma omp barrier
   return ret;
diff --git a/nestkernel/per_thread_bool_indicator.h b/nestkernel/per_thread_bool_indicator.h
index b5178002d1..bafd79a307 100644
--- a/nestkernel/per_thread_bool_indicator.h
+++ b/nestkernel/per_thread_bool_indicator.h
@@ -24,6 +24,7 @@
 #define PER_THREAD_BOOL_INDICATOR_H
 
 // C++ includes:
+#include <atomic>
 #include <cassert>
 #include <cstddef>
 #include <cstdint>
@@ -165,8 +166,8 @@ class PerThreadBoolIndicator
 
 private:
   std::vector< BoolIndicatorUInt64 > per_thread_status_;
-  std::atomic< int > size_ { 0 };
-  
+  int size_ { 0 };
+
   /** Number of per-thread indicators currently true
    *
    * are_true_ == 0 -> all are false