diff --git a/src/OpenFOAM/matrices/LLTMatrix/LLTMatrix.H b/src/OpenFOAM/matrices/LLTMatrix/LLTMatrix.H
index 622efc5a62..fa60845fa7 100644
--- a/src/OpenFOAM/matrices/LLTMatrix/LLTMatrix.H
+++ b/src/OpenFOAM/matrices/LLTMatrix/LLTMatrix.H
@@ -74,7 +74,8 @@ public:
         void decompose(const SquareMatrix<Type>& M);
 
         //- Solve the linear system with the given source
-        //  and returning the solution in the Field argument x
+        //  and returning the solution in the Field argument x.
+        //  This function may be called with the same field for x and source.
         void solve(Field<Type>& x, const Field<Type>& source) const;
 
         //- Solve the linear system with the given source