diff --git a/ChangeLog b/ChangeLog
index 0e89b33..da4d2b3 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,10 +1,11 @@
-2014-01-21  Juergen Knoedlseder  <jurgen.knodlseder@irap.omp.eu>
+2014-01-24  Juergen Knoedlseder  <jurgen.knodlseder@irap.omp.eu>
         
         * Bug fix Version 0.7.1 released
         ================================
         
         Added missing hyphens in pfiles synchronisation section (#1091)
         Add configuration test script (#1091)
+        Correctly filter instrument and id attributes in ctobssim
 
 
 2014-01-18  Juergen Knoedlseder  <jurgen.knodlseder@irap.omp.eu>
diff --git a/NEWS b/NEWS
index a6e0c6d..8dd3246 100644
--- a/NEWS
+++ b/NEWS
@@ -2,7 +2,7 @@ New Features and Important Changes in ctools 00-07-01
 
 Author(s) : Juergen Knoedlseder
 
-21 January 2014
+24 January 2014
 
 
 1. Introduction
@@ -29,7 +29,10 @@ None
 
 4. ctobssim - CTA observation simulation
 ----------------------------------------
-None
+The instrument and id attributes provided by an observation were not
+considering when simulating source and background events. This has been
+changed now that only events will be simulated when the instrument
+and id are valid for a given model.
 
 
 5. ctselect - CTA event selection
diff --git a/src/ctobssim/ctobssim.cpp b/src/ctobssim/ctobssim.cpp
index 9c1a0f7..6163a60 100644
--- a/src/ctobssim/ctobssim.cpp
+++ b/src/ctobssim/ctobssim.cpp
@@ -689,8 +689,10 @@ void ctobssim::simulate_source(GCTAObservation* obs, const GModels& models,
                     const GModelSky* model =
                           dynamic_cast<const GModelSky*>(models[i]);
 
-                    // If we have a sky model then simulate photons
-                    if (model != NULL) {
+                    // If we have a sky model that applies to the present
+                    // observation then simulate events
+                    if (model != NULL &&
+                        model->is_valid(obs->instrument(), obs->id())) {
 
                         // Determine duration of a time slice by limiting the
                         // number of simulated photons to m_max_photons.
@@ -896,9 +898,10 @@ void ctobssim::simulate_background(GCTAObservation* obs,
             const GModelData* model =
                 dynamic_cast<const GModelData*>(models[i]);
 
-            // If we have a data model that applies to CTA then simulate
-            // events
-            if (model != NULL && model->is_valid("CTA", "")) {
+            // If we have a data model that applies to the present observation
+            // then simulate events
+            if (model != NULL &&
+                model->is_valid(obs->instrument(), obs->id())) {
 
                 // Get simulated CTA event list. Note that this method
                 // includes the deadtime correction.