diff --git a/dune/istl/bcrsmatrix.hh b/dune/istl/bcrsmatrix.hh
index baff3c9e51d5ac6d362eaa57368a73e5e63537ea..c80cbd171a4e5bcb83adc16032887f87db26fb17 100644
--- a/dune/istl/bcrsmatrix.hh
+++ b/dune/istl/bcrsmatrix.hh
@@ -759,7 +759,7 @@ namespace Dune {
         avg(Mat.avg), overflowsize(Mat.overflowsize)
     {
       if (!(Mat.ready == notAllocated || Mat.ready == built))
-        DUNE_THROW(InvalidStateException,"BCRSMatrix can only be copied when both target and source are empty or fully built)");
+        DUNE_THROW(InvalidStateException,"BCRSMatrix can only be copy-constructed when source matrix is completely empty (size not set) or fully built)");
 
       // deep copy in global array
       size_type _nnz = Mat.nnz;