diff --git a/dirneucoupling.cc b/dirneucoupling.cc
index 6eb19fd75d4d68978abdc07a5ae51d26da7116f2..1ca7ba9b4afe758371679d6954b87eafa462f2a5 100644
--- a/dirneucoupling.cc
+++ b/dirneucoupling.cc
@@ -477,7 +477,7 @@ int main (int argc, char *argv[]) try
 
     // Store the history of total conv rates so we can filter out numerical
     // dirt in the end.
-    std::vector<double> totalConvRate(maxDirichletNeumannSteps);
+    std::vector<double> totalConvRate(maxDirichletNeumannSteps+1);
     totalConvRate[0] = 1;