diff --git a/preface.tex b/preface.tex
index 95a947e..eebd89c 100644
--- a/preface.tex
+++ b/preface.tex
@@ -28,6 +28,6 @@ You can always send feedback on the book to
 \texttt{ahslaaks@cs.helsinki.fi}.
 
 \begin{flushright}
-Helsinki, April 2017 \\
+Helsinki, May 2017 \\
 Antti Laaksonen
 \end{flushright}