diff --git a/a/dist/sink.spec b/b/dist/sink.spec
--- a/a/dist/sink.spec
+++ b/b/dist/sink.spec
@@ -17,6 +17,7 @@
 BuildRequires:  kf5-kcoreaddons-devel
 BuildRequires:  kf5-kcontacts-devel
 BuildRequires:  kf5-kmime-devel
+BuildRequires:  kf5-kcalendarcore-devel
 BuildRequires:  kimap2-devel >= 0.2
 BuildRequires:  kdav2-devel
 BuildRequires:  libcurl-devel