diff --git a/src/KSPACE/pppm.cpp b/src/KSPACE/pppm.cpp
index d09b638fe5..6778efbb35 100644
--- a/src/KSPACE/pppm.cpp
+++ b/src/KSPACE/pppm.cpp
@@ -1357,7 +1357,7 @@ void PPPM::compute_gf_denom()
     gf_b[0] = 4.0 * (gf_b[0]*(l-m)*(l-m-0.5));
   }
 
-  int ifact = 1;
+  bigint ifact = 1;
   for (k = 1; k < 2*order; k++) ifact *= k;
   double gaminv = 1.0/ifact;
   for (l = 0; l < order; l++) gf_b[l] *= gaminv;
diff --git a/src/KSPACE/pppm_old.cpp b/src/KSPACE/pppm_old.cpp
index 6f98a4c2ab..0b7f2d45e3 100644
--- a/src/KSPACE/pppm_old.cpp
+++ b/src/KSPACE/pppm_old.cpp
@@ -1194,7 +1194,7 @@ void PPPMOld::compute_gf_denom()
     gf_b[0] = 4.0 * (gf_b[0]*(l-m)*(l-m-0.5));
   }
 
-  int ifact = 1;
+  bigint ifact = 1;
   for (k = 1; k < 2*order; k++) ifact *= k;
   double gaminv = 1.0/ifact;
   for (l = 0; l < order; l++) gf_b[l] *= gaminv;