diff --git a/src/pair.cpp b/src/pair.cpp
index 65039615e3..a9062e315e 100644
--- a/src/pair.cpp
+++ b/src/pair.cpp
@@ -1436,6 +1436,10 @@ void Pair::virial_fdotr_compute()
     }
   }
   
+  // prevent multiple calls to update the virial
+  // when a hybrid pair style uses both a gpu and non-gpu pair style
+  // or when respa is used with gpu pair styles
+
   vflag_fdotr = 0;
 }