diff --git a/modules/Bio/EnsEMBL/AssemblyMapper.pm b/modules/Bio/EnsEMBL/AssemblyMapper.pm
index 5ed9941be6ae55f01342a8463e7111c71c82d3d7..2d4a9b8a9021bf50f58c169b9c2a8ac118bec960 100644
--- a/modules/Bio/EnsEMBL/AssemblyMapper.pm
+++ b/modules/Bio/EnsEMBL/AssemblyMapper.pm
@@ -97,7 +97,7 @@ sub new {
 
   $self->adaptor($adaptor);
 
-  #$adaptor->cache_seq_ids_with_mult_assemblys();
+  $adaptor->cache_seq_ids_with_mult_assemblys();
 
   if(@coord_systems != 2) {
     throw('Can only map between 2 coordinate systems. ' .
diff --git a/modules/Bio/EnsEMBL/ChainedAssemblyMapper.pm b/modules/Bio/EnsEMBL/ChainedAssemblyMapper.pm
index 7a38974304f06b86d24b2c4953bc411f2b23b2e9..5009716832bb62d3425998001935eb733b8d1cf6 100644
--- a/modules/Bio/EnsEMBL/ChainedAssemblyMapper.pm
+++ b/modules/Bio/EnsEMBL/ChainedAssemblyMapper.pm
@@ -111,7 +111,7 @@ sub new {
           scalar(@coord_systems) . ' were provided');
   }
 
-  #$adaptor->cache_seq_ids_with_mult_assemblys();
+  $adaptor->cache_seq_ids_with_mult_assemblys();
 
   # Set the component, intermediate and assembled coordinate systems
   $self->{'first_cs'}   = $coord_systems[0];