diff --git a/ChangeLog b/ChangeLog
index e058c7c..6ef4396 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,9 +1,10 @@
-2014-06-26  Juergen Knoedlseder  <jurgen.knodlseder@irap.omp.eu>
+2014-07-09  Juergen Knoedlseder  <jurgen.knodlseder@irap.omp.eu>
 
         * Version 0.8.0 released
         ========================
 
         Support energy dispersion in ctobssim, ctlike and ctmodel	
+        Correct ctobssim for thread safety
         Enhance documentation
 
 
diff --git a/NEWS b/NEWS
index 7c72ca8..37037b8 100644
--- a/NEWS
+++ b/NEWS
@@ -2,7 +2,7 @@ New Features and Important Changes in ctools 00-08-00
 
 Author(s) : Juergen Knoedlseder
 
-26 June 2014
+9 July 2014
 
 
 1. Introduction
@@ -23,7 +23,10 @@ None
 
 4. ctobssim - CTA observation simulation
 ----------------------------------------
-None
+ctobssim was not fully thread save as the models were shared among the
+threads which led to concurrent memory access when evaluating the Monte
+Carlo cache. The models are now copied within the parallel section,
+avoiding concurrent memory access (#1258).
 
 ctobssim now also supports the handling of energy dispersion. Energy
 dispersion can be switched on or off using the hidden edisp parameter.
diff --git a/src/ctobssim/ctobssim.cpp b/src/ctobssim/ctobssim.cpp
index 29f353d..ae1c7fb 100644
--- a/src/ctobssim/ctobssim.cpp
+++ b/src/ctobssim/ctobssim.cpp
@@ -305,6 +305,9 @@ void ctobssim::run(void)
             wrklog.cout(true);
         }
 
+        // Allocate and initialize copies for multi-threading
+        GModels models(m_obs.models());
+
         // Copy configuration from application logger to thread logger
         wrklog.date(log.date());
         wrklog.name(log.name());
@@ -340,10 +343,10 @@ void ctobssim::run(void)
                 int events_before = obs->events()->size();
 
                 // Simulate source events
-                simulate_source(obs, m_obs.models(), m_rans[i], &wrklog);
+                simulate_source(obs, models, m_rans[i], &wrklog);
 
                 // Simulate source events
-                simulate_background(obs, m_obs.models(), m_rans[i], &wrklog);
+                simulate_background(obs, models, m_rans[i], &wrklog);
 
                 // Dump simulation results
                 if (logNormal()) {