diff --git a/numapde.bib b/numapde.bib
index 800b0c4e0a12297656794c6f1038e84020459c5b..81af84587907d43483567184bb67f4935e2d890b 100644
--- a/numapde.bib
+++ b/numapde.bib
@@ -44545,3 +44545,14 @@
   TITLE = {The Numerical Solution of Two-Factor Option Pricing Models},
   TYPE = {phdthesis},
 }
+@ARTICLE{KroenerVexler:2009:1,
+    AUTHOR = "Kröner, Axel and Vexler, Boris",
+    PUBLISHER = "Elsevier BV",
+    DATE = "2009-08",
+    DOI = "10.1016/j.cam.2009.01.023",
+    JOURNALTITLE = "Journal of Computational and Applied Mathematics",
+    NUMBER = "2",
+    PAGES = "781--802",
+    TITLE = "A priori error estimates for elliptic optimal control problems with a bilinear state equation",
+    VOLUME = "230"
+}