diff --git a/core/output.py b/core/output.py
index d75f285..2d12443 100644
--- a/core/output.py
+++ b/core/output.py
@@ -26,7 +26,6 @@ def __init__(self, param, grid, diag, flxlist=None):
         self.template = self.expdir+'/%s_his_%03i.nc'
         if self.nbproc > 1:
             self.hisfile = self.template % (self.expname, self.myrank)
-            self.hisfile_joined = '%s/%s_his.nc' % (self.expdir, self.expname)
         else:
             self.hisfile = '%s/%s_his.nc' % (self.expdir, self.expname)
 
@@ -43,7 +42,6 @@ def __init__(self, param, grid, diag, flxlist=None):
             template = self.expdir+'/%s_flx_%03i.nc'
             if self.nbproc > 1:
                 self.flxfile = template % (self.expname, self.myrank)
-                self.flxfile_joined = '%s/%s_flx.nc' % (self.expdir, self.expname)
             else:
                 self.flxfile = '%s/%s_flx.nc' % (self.expdir, self.expname)
 
@@ -154,13 +152,13 @@ def dump_diag(self):
     def join(self):
         if self.nbproc > 1:
             filename = self.hisfile.split('his')[0]+'his'
-            join(filename)
+            self.hisfile = join(filename)
             if self.diag_fluxes:
                 filename = self.flxfile.split('flx')[0]+'flx'
-                join(filename)
-                
-            
-            
+                self.flxfile = join(filename)
+
+
+
 class NcfileIO(object):
     """Allow to create() and write() a Netcdf file of 'history' type,
     i.e. a set of model 2D snapshots. Variables were originally the
@@ -250,7 +248,8 @@ def join(filename):
     ''' Join history files without having to mpirun
 
     Useful when the run has been broken and one wants to join
-    things from an interactive session '''
+    things from an interactive session.
+    Return the name of the new, joined history file. '''
 
     template = filename+'_%03i.nc'
     hisfile_joined = filename+'.nc'
@@ -390,3 +389,5 @@ def join(filename):
         os.remove(ncfile)
 
     print('-'*50)
+
+    return hisfile_joined
diff --git a/core/plotting.py b/core/plotting.py
index 296fee0..38ec41c 100644
--- a/core/plotting.py
+++ b/core/plotting.py
@@ -22,6 +22,14 @@ def __init__(self, param, grid, var, diag):
                            'generate_mp4', 'myrank', 'modelname']
         param.copy(self, self.list_param)
 
+        if param.npx * param.npy > 1 and self.generate_mp4:
+            print(
+                'Warning: It is not possible to generate an mp4-file when '
+                'fluid2d runs on multiple cores.\n'
+                'The parameter generate_mp4 is automatically changed to False.'
+            )
+            self.generate_mp4 = False
+
         nh = self.nh
         nx = param.nx
         ny = param.ny
diff --git a/core/restart.py b/core/restart.py
index c012a02..e3541f3 100644
--- a/core/restart.py
+++ b/core/restart.py
@@ -78,16 +78,10 @@ def __init__(self, param, grid, f2d, launch=True):
         f2d.output.template = self.expdir +'/%s_%02i_his' % (
             self.expname, self.nextrestart)+'_%03i.nc'
         f2d.output.hisfile = f2d.output.template % (self.myrank)
-        f2d.output.hisfile_joined = self.expdir + '/%s_%02i_his.nc' % (
-            self.expname, self.nextrestart)
         if self.diag_fluxes:
             f2d.output.template = self.expdir +'/%s_%02i_flx' % (
                 self.expname, self.nextrestart)+'_%03i.nc'
             f2d.output.flxfile = f2d.output.template % (self.myrank)
-            f2d.output.flxfile_joined = self.expdir + '/%s_%02i_flx.nc' % (
-                self.expname, self.nextrestart)
-            
-            
 
         # split the integration in 'ninterrestart' intervals and
         # save a restart at the end of each