diff --git a/dune/solvers/iterationsteps/cgstep.hh b/dune/solvers/iterationsteps/cgstep.hh
index 6d7bc3ecdc9badd8c366725fed8d359206ef45ef..354f55dee12b6489746a5621f8e3b3957f7a299c 100644
--- a/dune/solvers/iterationsteps/cgstep.hh
+++ b/dune/solvers/iterationsteps/cgstep.hh
@@ -43,6 +43,7 @@ namespace Dune {
                 this->setMatrix(mat);
                 setProblem(x);
                 r_ = rhs;
+                p_.resize(r_.size());
             }
 
             void check() const override;