Forgot the (trivial) patch. Here it is.
--- a/debian/control
+++ b/debian/control
@@ -19,7 +19,8 @@ XS-Ruby-Versions: all
Package: unicorn
Architecture: kfreebsd-any linux-any
XB-Ruby-Versions: ${ruby:Versions}
-Depends: ruby | ruby-interpreter,
+Depends: lsb-base,
+ ruby | ruby-interpreter,
ruby-kgio (>= 2.10.0~),
ruby-rack,
ruby-raindrops (>= 0.16.0~),
