diff --git a/mcstas-comps/misc/MCPL_input_once.comp b/mcstas-comps/misc/MCPL_input_once.comp
index 8c9c074ff3..805eb56939 100644
--- a/mcstas-comps/misc/MCPL_input_once.comp
+++ b/mcstas-comps/misc/MCPL_input_once.comp
@@ -179,6 +179,7 @@ TRACE
   
   if (current_index >= maximum_index){
     // go back to the start of this worker's particles, rather than accessing out-of-range data
+    #pragma acc atomic write
     current_index = 0;
 #ifndef OPENACC
     if (!preload){
@@ -208,8 +209,11 @@ TRACE
     if (!times_replayed) used_neutrons++;
   } else {
 #endif
-    ptr = particles + current_index++;
-#ifndef OPENACC
+    ptr = particles + (_particle->_uid % maximum_index);
+#ifdef OPENACC
+    #pragma acc atomic
+    current_index++; // track how many particles have been accessed, to ensure we don't exceed our slice of the file
+#else OPENACC
   }
 #endif
   // copy from the component particle struct to the particle ray struct:
@@ -217,6 +221,7 @@ TRACE
     fprintf(stderr, "ERROR (%s): component particle struct pointer not set! Crash before out-of-bounds memory access.\n", NAME_CURRENT_COMP);
     exit(-1);
   }
+  #pragma acc atomic
   emitted_neutrons++;
   // this could be done via memcpy if we ensure equal memory layout with the ray's struct
   x = ptr->_x;
diff --git a/mcstas-comps/union/Union_abs_logger_1D_space_event.comp b/mcstas-comps/union/Union_abs_logger_1D_space_event.comp
index d02bdc34db..f1dd0f332a 100644
--- a/mcstas-comps/union/Union_abs_logger_1D_space_event.comp
+++ b/mcstas-comps/union/Union_abs_logger_1D_space_event.comp
@@ -101,7 +101,8 @@ SHARE
 #error "The Union_init component must be included before this Union_abs_logger_1D_space_event component"
 #endif
 
-%include "monitor_nd-lib" // Internally avoids double import
+// Internally avoids double import
+%include "monitor_nd-lib"
 
 struct temp_abs_1D_event_data_element_struct {
  double x_pos;
diff --git a/mcstas-comps/union/Union_abs_logger_event.comp b/mcstas-comps/union/Union_abs_logger_event.comp
index d0315068c1..d3e5fb6ac6 100644
--- a/mcstas-comps/union/Union_abs_logger_event.comp
+++ b/mcstas-comps/union/Union_abs_logger_event.comp
@@ -85,7 +85,8 @@ SHARE
 #error "The Union_init component must be included before this Union_abs_logger_event component"
 #endif
 
-%include "monitor_nd-lib" // Internally avoids double import
+// Internally avoids double import
+%include "monitor_nd-lib"
 
 struct temp_abs_event_data_element_struct {
  double x_pos;