diff --git a/owlps-positioner/src/autocalibration.cc b/owlps-positioner/src/autocalibration.cc
index 3a9e413..dff62f5 100644
--- a/owlps-positioner/src/autocalibration.cc
+++ b/owlps-positioner/src/autocalibration.cc
@@ -115,6 +115,9 @@ void Autocalibration::sort_reference_aps()
 {
   const Point3D &rx_coord = rx->second.get_coordinates() ;
 
+  sorted_negative_angles.clear() ;
+  sorted_positive_angles.clear() ;
+
   for (unordered_map<string, AccessPoint>::const_iterator
        ref = Stock::aps.begin() ; ref != Stock::aps.end() ; ++ref)
     {
@@ -165,6 +168,7 @@ void Autocalibration::sort_reference_aps()
 void Autocalibration::weight_aps()
 {
   /* Retrieve the reference APs & angles */
+  ref_aps.clear() ;
   map<double, pair<double,
       unordered_map<string, AccessPoint>::const_iterator> >
       ::const_iterator s ;
@@ -181,8 +185,12 @@ void Autocalibration::weight_aps()
   else if (ref_aps.size() == 2)
     weight_2_aps() ;
   else
-    throw autocalibration_error(
-      "We should not be here... error when sorting the reference APs?") ;
+    {
+      ostringstream oss ;
+      oss << "We should not be here... error when sorting the reference"
+          << " APs? (" << ref_aps.size() << " APs sorted)" ;
+      throw autocalibration_error(oss.str()) ;
+    }
 }