diff --git a/source/source_pw/module_pwdft/soc.cpp b/source/source_pw/module_pwdft/soc.cpp
index a96c7ad235..dae307617c 100644
--- a/source/source_pw/module_pwdft/soc.cpp
+++ b/source/source_pw/module_pwdft/soc.cpp
@@ -27,18 +27,19 @@ void Fcoef::create(const int i1, const int i2, const int i3)
     }
     else
     {
-        std::cout << "not allowed!" << std::endl;
+        std::cout << "Fcoef::create: not allowed!" << std::endl;
         if (!(i1 * i2 * i3 > 0)){
-            std::cout << "i1*i2*i3 must be positive! i1*i2*i3 is " << i1 * i2 * i3 << std::endl;
+            unsigned long long product = static_cast<unsigned long long>(i1) * static_cast<unsigned long long>(i2) * static_cast<unsigned long long>(i3);
+            std::cout << "Fcoef::create: possible integer overflow in product i1*i2*i3! i1 is " << i1 << ", i2 is " << i2 << ", i3 is " << i3 << ", product is " << product << std::endl;
         }
         if (!(i1 > 0)){
-            std::cout << "i1 must be positive! i1 is " << i1 << std::endl;
+            std::cout << "Fcoef::create: i1 must be positive! i1 is " << i1 << std::endl;
         }
         if (!(i2 > 0)){
-            std::cout << "i2 must be positive! i2 is " << i2 << std::endl;
+            std::cout << "Fcoef::create: i2 must be positive! i2 is " << i2 << std::endl;
         }
         if (!(i3 > 0)){
-            std::cout << "i3 must be positive! i3 is " << i3 << std::endl;
+            std::cout << "Fcoef::create: i3 must be positive! i3 is " << i3 << std::endl;
         }
 
     }