diff --git a/src/fix_external.cpp b/src/fix_external.cpp
index fffc57c72c..a09dd62ffd 100644
--- a/src/fix_external.cpp
+++ b/src/fix_external.cpp
@@ -33,6 +33,10 @@ FixExternal::FixExternal(LAMMPS *lmp, int narg, char **arg) :
 {
   if (narg < 4) error->all(FLERR,"Illegal fix external command");
 
+  scalar_flag = 1;
+  global_freq = 1;
+  extscalar = 1;
+
   if (strcmp(arg[3],"pf/callback") == 0) {
     if (narg != 6) error->all(FLERR,"Illegal fix external command");
     mode = PF_CALLBACK;
@@ -55,6 +59,8 @@ FixExternal::FixExternal(LAMMPS *lmp, int narg, char **arg) :
   fexternal = NULL;
   grow_arrays(atom->nmax);
   atom->add_callback(0);
+
+  user_energy = 0.0;
 }
 
 /* ---------------------------------------------------------------------- */
@@ -75,6 +81,7 @@ int FixExternal::setmask()
   int mask = 0;
   if (mode == PF_CALLBACK || mode == PF_ARRAY) {
     mask |= POST_FORCE;
+    mask |= THERMO_ENERGY;
     mask |= MIN_POST_FORCE;
   }
   return mask;
@@ -138,6 +145,23 @@ void FixExternal::min_post_force(int vflag)
   post_force(vflag);
 }
 
+/* ---------------------------------------------------------------------- */
+
+void FixExternal::set_energy(double eng)
+{
+  user_energy = eng;
+}
+
+/* ----------------------------------------------------------------------
+   potential energy of added force
+   up to user to set it via set_energy()
+------------------------------------------------------------------------- */
+
+double FixExternal::compute_scalar()
+{
+  return user_energy;
+}
+
 /* ----------------------------------------------------------------------
    memory usage of local atom-based array
 ------------------------------------------------------------------------- */
diff --git a/src/fix_external.h b/src/fix_external.h
index fdd32b7712..3e38f09c42 100644
--- a/src/fix_external.h
+++ b/src/fix_external.h
@@ -26,6 +26,8 @@ namespace LAMMPS_NS {
 
 class FixExternal : public Fix {
  public:
+  double **fexternal;
+
   FixExternal(class LAMMPS *, int, char **);
   ~FixExternal();
   int setmask();
@@ -34,6 +36,9 @@ class FixExternal : public Fix {
   void min_setup(int);
   void post_force(int);
   void min_post_force(int);
+  double compute_scalar();
+
+  void set_energy(double eng);
 
   double memory_usage();
   void grow_arrays(int);
@@ -48,7 +53,7 @@ class FixExternal : public Fix {
   int mode,ncall,napply;
   FnPtr callback;
   void *ptr_caller;
-  double **fexternal;
+  double user_energy;
 };
 
 }