diff --git a/src/PYTHON/fix_python_invoke.cpp b/src/PYTHON/fix_python_invoke.cpp
index 6483e21f91..7d981a749e 100644
--- a/src/PYTHON/fix_python_invoke.cpp
+++ b/src/PYTHON/fix_python_invoke.cpp
@@ -92,8 +92,9 @@ int FixPythonInvoke::setmask()
 void FixPythonInvoke::end_of_step()
 {
   PyUtils::GIL lock;
+  char fmt[] = "O";
 
-  PyObject * result = PyObject_CallFunction((PyObject*)pFunc, "O", (PyObject*)lmpPtr);
+  PyObject * result = PyObject_CallFunction((PyObject*)pFunc, fmt, (PyObject*)lmpPtr);
 
   if (!result) {
     PyUtils::Print_Errors();
@@ -110,8 +111,9 @@ void FixPythonInvoke::post_force(int vflag)
   if (update->ntimestep % nevery != 0) return;
 
   PyUtils::GIL lock;
+  char fmt[] = "Oi";
 
-  PyObject * result = PyObject_CallFunction((PyObject*)pFunc, "Oi", (PyObject*)lmpPtr, vflag);
+  PyObject * result = PyObject_CallFunction((PyObject*)pFunc, fmt, (PyObject*)lmpPtr, vflag);
 
   if (!result) {
     PyUtils::Print_Errors();
diff --git a/src/PYTHON/fix_python_move.cpp b/src/PYTHON/fix_python_move.cpp
index e04a32afe4..8ec2e1b74d 100644
--- a/src/PYTHON/fix_python_move.cpp
+++ b/src/PYTHON/fix_python_move.cpp
@@ -75,7 +75,7 @@ FixPythonMove::FixPythonMove(LAMMPS *lmp, int narg, char **arg) :
   }
 
   PyObject *ptr = PY_VOID_POINTER(lmp);
-  PyObject *py_move_obj = PyObject_CallFunction(py_move_type, "O", ptr);
+  PyObject *py_move_obj = PyObject_CallFunction(py_move_type, (char *)"O", ptr);
   Py_CLEAR(ptr);
 
   if (!py_move_obj) {
@@ -112,7 +112,7 @@ int FixPythonMove::setmask()
 void FixPythonMove::init()
 {
   PyUtils::GIL lock;
-  PyObject * result = PyObject_CallMethod((PyObject *)py_move, "init", nullptr);
+  PyObject * result = PyObject_CallMethod((PyObject *)py_move, (char *)"init", nullptr);
 
   if (!result) {
     PyUtils::Print_Errors();
@@ -126,7 +126,7 @@ void FixPythonMove::init()
 void FixPythonMove::initial_integrate(int vflag)
 {
   PyUtils::GIL lock;
-  PyObject * result = PyObject_CallMethod((PyObject*)py_move, "initial_integrate", "i", vflag);
+  PyObject * result = PyObject_CallMethod((PyObject*)py_move, (char *)"initial_integrate", (char *)"i", vflag);
 
   if (!result) {
     PyUtils::Print_Errors();
@@ -140,7 +140,7 @@ void FixPythonMove::initial_integrate(int vflag)
 void FixPythonMove::final_integrate()
 {
   PyUtils::GIL lock;
-  PyObject * result = PyObject_CallMethod((PyObject*)py_move, "final_integrate", nullptr);
+  PyObject * result = PyObject_CallMethod((PyObject*)py_move, (char *)"final_integrate", nullptr);
 
   if (!result) {
     PyUtils::Print_Errors();
@@ -154,7 +154,7 @@ void FixPythonMove::final_integrate()
 void FixPythonMove::initial_integrate_respa(int vflag, int ilevel, int iloop)
 {
   PyUtils::GIL lock;
-  PyObject * result = PyObject_CallMethod((PyObject*)py_move, "initial_integrate_respa", "iii", vflag, ilevel, iloop);
+  PyObject * result = PyObject_CallMethod((PyObject*)py_move, (char *)"initial_integrate_respa", (char *)"iii", vflag, ilevel, iloop);
 
   if (!result) {
     PyUtils::Print_Errors();
@@ -168,7 +168,7 @@ void FixPythonMove::initial_integrate_respa(int vflag, int ilevel, int iloop)
 void FixPythonMove::final_integrate_respa(int ilevel, int iloop)
 {
   PyUtils::GIL lock;
-  PyObject * result = PyObject_CallMethod((PyObject*)py_move, "final_integrate_respa", "ii", ilevel, iloop);
+  PyObject * result = PyObject_CallMethod((PyObject*)py_move, (char *)"final_integrate_respa", (char *)"ii", ilevel, iloop);
 
   if (!result) {
     PyUtils::Print_Errors();
@@ -182,7 +182,7 @@ void FixPythonMove::final_integrate_respa(int ilevel, int iloop)
 void FixPythonMove::reset_dt()
 {
   PyUtils::GIL lock;
-  PyObject * result = PyObject_CallMethod((PyObject*)py_move, "reset_dt", nullptr);
+  PyObject * result = PyObject_CallMethod((PyObject*)py_move, (char *)"reset_dt", nullptr);
 
   if (!result) {
     PyUtils::Print_Errors();
diff --git a/src/PYTHON/pair_python.cpp b/src/PYTHON/pair_python.cpp
index b147c9cb79..5020119e0d 100644
--- a/src/PYTHON/pair_python.cpp
+++ b/src/PYTHON/pair_python.cpp
@@ -288,7 +288,7 @@ void PairPython::coeff(int narg, char **arg)
 
   py_potential = (void *) py_pair_instance;
 
-  PyObject *py_value = PyObject_CallMethod(py_pair_instance, "check_units", "s", update->unit_style);
+  PyObject *py_value = PyObject_CallMethod(py_pair_instance, (char *)"check_units", (char *)"s", update->unit_style);
   if (!py_value) {
     PyUtils::Print_Errors();
     error->all(FLERR,"Calling 'check_units' function failed");
@@ -306,7 +306,7 @@ void PairPython::coeff(int narg, char **arg)
     } else skip_types[i] = 0;
     const int type = i;
     const char * name = arg[2+i];
-    py_value = PyObject_CallMethod(py_pair_instance, "map_coeff", "si", name, type);
+    py_value = PyObject_CallMethod(py_pair_instance, (char *)"map_coeff", (char *)"si", name, type);
     if (!py_value) {
       PyUtils::Print_Errors();
       error->all(FLERR,"Calling 'map_coeff' function failed");