diff --git a/Cantera/src/base/ct_defs.h b/Cantera/src/base/ct_defs.h
index e24d6663c..d00f8fff1 100755
--- a/Cantera/src/base/ct_defs.h
+++ b/Cantera/src/base/ct_defs.h
@@ -146,6 +146,7 @@ namespace Cantera {
     const doublereal SqrtTen = std::sqrt(10.0);
   //! sqrt(8)
     const doublereal SqrtEight = std::sqrt(8.0);
+  //! sqrt(2)
     const doublereal SqrtTwo = std::sqrt(2.0);
 
   //! smallest number to compare to zero.