diff --git a/src/KSPACE/ewald.cpp b/src/KSPACE/ewald.cpp
index d41443f02a..c7d242031f 100644
--- a/src/KSPACE/ewald.cpp
+++ b/src/KSPACE/ewald.cpp
@@ -154,6 +154,8 @@ void Ewald::init()
   if (!gewaldflag) {
     if (accuracy <= 0.0)
       error->all(FLERR,"KSpace accuracy must be > 0");
+    if (q2 == 0.0)
+      error->all(FLERR,"Must use 'kspace_modify gewald' for uncharged system");
     g_ewald = accuracy*sqrt(natoms*cutoff*xprd*yprd*zprd) / (2.0*q2);
     if (g_ewald >= 1.0) g_ewald = (1.35 - 0.15*log(accuracy))/cutoff;
     else g_ewald = sqrt(-log(g_ewald)) / cutoff;
@@ -340,6 +342,7 @@ void Ewald::setup()
 
 double Ewald::rms(int km, double prd, bigint natoms, double q2)
 {
+  if (natoms == 0) natoms = 1;   // avoid division by zero
   double value = 2.0*q2*g_ewald/prd *
     sqrt(1.0/(MY_PI*km*natoms)) *
     exp(-MY_PI*MY_PI*km*km/(g_ewald*g_ewald*prd*prd));
diff --git a/src/KSPACE/ewald_disp.cpp b/src/KSPACE/ewald_disp.cpp
index 85e3da921b..e0424b0d93 100644
--- a/src/KSPACE/ewald_disp.cpp
+++ b/src/KSPACE/ewald_disp.cpp
@@ -193,6 +193,10 @@ void EwaldDisp::init()
 
   if (!gewaldflag) {
     if (function[0]) {
+      if (accuracy <= 0.0)
+        error->all(FLERR,"KSpace accuracy must be > 0");
+      if (q2 == 0.0)
+        error->all(FLERR,"Must use 'kspace_modify gewald' for uncharged system");
       g_ewald = accuracy*sqrt(natoms*(*cutoff)*shape_det(domain->h)) / (2.0*q2);
       if (g_ewald >= 1.0) g_ewald = (1.35 - 0.15*log(accuracy))/(*cutoff);
       else g_ewald = sqrt(-log(g_ewald)) / (*cutoff);
@@ -298,6 +302,7 @@ double EwaldDisp::rms(int km, double prd, bigint natoms,
                       double q2, double b2, double M2)
 {
   double value = 0.0;
+  if (natoms == 0) natoms = 1; // avoid division by zero
 
   // Coulombic