diff --git a/src/compute.cpp b/src/compute.cpp
index a12373fd51..5d5a4d5246 100644
--- a/src/compute.cpp
+++ b/src/compute.cpp
@@ -59,6 +59,7 @@ Compute::Compute(LAMMPS *lmp, int narg, char **arg) :
   // set child class defaults
 
   scalar_flag = vector_flag = array_flag = 0;
+  extscalar = extvector = extarray = -1;
   peratom_flag = local_flag = pergrid_flag = 0;
   size_vector_variable = size_array_rows_variable = 0;
 
@@ -116,6 +117,16 @@ void Compute::init_flags()
   initialized_flag = 1;
   invoked_scalar = invoked_vector = invoked_array = -1;
   invoked_peratom = invoked_local = -1;
+
+  if (scalar_flag && (extscalar < 0))
+    error->all(FLERR, "Must set 'extscalar' when setting 'scalar_flag' for compute {}.  "
+               "Contact the developer.", style);
+  if (vector_flag && (extvector < 0))
+    error->all(FLERR, "Must set 'extvector' when setting 'vector_flag' for compute {}.  "
+               "Contact the developer.", style);
+  if (array_flag && (extarray < 0))
+    error->all(FLERR, "Must set 'extarray' when setting 'array_flag' for compute {}.  "
+               "Contact the developer.", style);
 }
 
 /* ---------------------------------------------------------------------- */
diff --git a/src/fix.cpp b/src/fix.cpp
index 754948fdd1..1e1ab8c928 100644
--- a/src/fix.cpp
+++ b/src/fix.cpp
@@ -81,6 +81,7 @@ Fix::Fix(LAMMPS *lmp, int /*narg*/, char **arg) :
   diam_flag = 0;
 
   scalar_flag = vector_flag = array_flag = 0;
+  extscalar = extvector = extarray = -1;
   peratom_flag = local_flag = pergrid_flag = 0;
   global_freq = local_freq = peratom_freq = pergrid_freq = -1;
   size_vector_variable = size_array_rows_variable = 0;
@@ -119,13 +120,28 @@ Fix::~Fix()
 {
   if (copymode) return;
 
-  delete [] id;
-  delete [] style;
+  delete[] id;
+  delete[] style;
   memory->destroy(eatom);
   memory->destroy(vatom);
   memory->destroy(cvatom);
 }
 
+/* ---------------------------------------------------------------------- */
+
+void Fix::init_flags()
+{
+   if (scalar_flag && (extscalar < 0))
+    error->all(FLERR, "Must set 'extscalar' when setting 'scalar_flag' for fix {}.  "
+               "Contact the developer.", style);
+  if (vector_flag && (extvector < 0))
+    error->all(FLERR, "Must set 'extvector' when setting 'vector_flag' for fix {}.  "
+               "Contact the developer.", style);
+  if (array_flag && (extarray < 0))
+    error->all(FLERR, "Must set 'extarray' when setting 'array_flag' for fix {}.  "
+               "Contact the developer.", style);
+}
+
 /* ----------------------------------------------------------------------
    process params common to all fixes here
    if unknown param, call modify_param specific to the fix
diff --git a/src/fix.h b/src/fix.h
index ca0a1ef84b..594fbb51bf 100644
--- a/src/fix.h
+++ b/src/fix.h
@@ -145,6 +145,7 @@ class Fix : protected Pointers {
 
   virtual void post_constructor() {}
   virtual void init() {}
+  void init_flags();
   virtual void init_list(int, class NeighList *) {}
   virtual void setup(int) {}
   virtual void setup_pre_exchange() {}
diff --git a/src/modify.cpp b/src/modify.cpp
index ba04c5969a..1a9c056027 100644
--- a/src/modify.cpp
+++ b/src/modify.cpp
@@ -188,6 +188,8 @@ void Modify::init()
   //   since any of them may be invoked by initial thermo
   // do not clear out invocation times stored within a compute,
   //   b/c some may be holdovers from previous run, like for ave fixes
+  // perform check whether extscalar, extvector, and extarray have been
+  //   set when scalar_flag, vector_flag, or array_flag are true.
 
   for (i = 0; i < ncompute; i++) {
     compute[i]->init();
@@ -200,8 +202,13 @@ void Modify::init()
   //   used to b/c temperature computes called fix->dof() in their init,
   //   and fix rigid required its own init before its dof() could be called,
   //   but computes now do their DOF in setup()
+  // perform check whether extscalar, extvector, and extarray have been
+  //   set when scalar_flag, vector_flag, or array_flag are true.
 
-  for (i = 0; i < nfix; i++) fix[i]->init();
+  for (i = 0; i < nfix; i++) {
+    fix[i]->init();
+    fix[i]->init_flags();
+  }
 
   // set global flag if any fix has its restart_pbc flag set