diff --git a/src/KSPACE/pppm.cpp b/src/KSPACE/pppm.cpp
index 2f5b4fc670..328c2c2362 100644
--- a/src/KSPACE/pppm.cpp
+++ b/src/KSPACE/pppm.cpp
@@ -1944,7 +1944,8 @@ void PPPM::poisson_ik()
 
   // global energy and virial contribution
 
-  double scaleinv = 1.0/(nx_pppm*ny_pppm*nz_pppm);
+  bigint ngridtotal = (bigint) nx_pppm * ny_pppm * nz_pppm;
+  double scaleinv = 1.0/(ngridtotal);
   double s2 = scaleinv*scaleinv;
 
   if (eflag_global || vflag_global) {
@@ -2145,7 +2146,8 @@ void PPPM::poisson_ad()
 
   // global energy and virial contribution
 
-  double scaleinv = 1.0/(nx_pppm*ny_pppm*nz_pppm);
+  bigint ngridtotal = (bigint) nx_pppm * ny_pppm * nz_pppm;
+  double scaleinv = 1.0/(ngridtotal);
   double s2 = scaleinv*scaleinv;
 
   if (eflag_global || vflag_global) {
@@ -3259,7 +3261,8 @@ void PPPM::poisson_groups(int AA_flag)
   //  keep everything in reciprocal space so
   //  no inverse FFTs needed
 
-  double scaleinv = 1.0/(nx_pppm*ny_pppm*nz_pppm);
+  bigint ngridtotal = (bigint) nx_pppm * ny_pppm * nz_pppm;
+  double scaleinv = 1.0/(ngridtotal);
   double s2 = scaleinv*scaleinv;
 
   // energy