diff --git a/debian/templates/control.source.in b/debian/templates/control.source.in
index c8d803c5d..f82c9b266 100644
--- a/debian/templates/control.source.in
+++ b/debian/templates/control.source.in
@@ -5,16 +5,27 @@ Uploaders: Bastian Blank <waldi@debian.org>, maximilian attems <maks@debian.org>
 Standards-Version: 3.9.5
 Build-Depends:
  debhelper,
+# used to run debian/bin/*.py
  python3:any,
+# used by debian/rules.real to prepare the source
  quilt,
+# used by debian/rules.real to build linux-doc and linux-headers
  cpio <!stage1>,
- kmod <!stage1>,
+# used by upstream to compress kernel and by debian/rules.real to build linux-source
  xz-utils <!stage1>,
+# used by debian/rules.real to build udebs
  kernel-wedge (>= 2.93~) <!stage1>,
+# used by kernel-wedge (only on Linux, thus not declared as a dependency)
+ kmod <!stage1>,
+# used by upstream to build include/generated/timeconst.h
  bc <!stage1>,
+# used by upstream to build signing tools and to process certificates
  libssl-dev <!stage1>,
  openssl <!stage1>,
+# used by upstream to build perf documentation
  asciidoc <!stage1>,
+ xmlto <!stage1>,
+# used by upstream to build perf
  bison <!stage1>,
  flex <!stage1>,
  gcc-multilib [amd64 ppc64 s390x sparc64] <!stage1>,
@@ -27,18 +38,23 @@ Build-Depends:
  libperl-dev <!stage1>,
  libunwind8-dev [amd64 armel armhf arm64 i386] <!stage1>,
  python-dev <!stage1>,
- xmlto <!stage1>,
+# used by upstream to build usbip
  autoconf <!stage1>,
  automake <!stage1>,
  libtool <!stage1>,
  libglib2.0-dev <!stage1>,
  libudev-dev <!stage1>,
  libwrap0-dev <!stage1>,
+# used by upstream to build cpupower
  libpci-dev <!stage1>,
+# used by debian/rules.real to build linux-perf and linux-support
  dh-python <!stage1>,
+# used by debian/rules.real to build hyperv-daemons
  dh-systemd <!stage1>,
 Build-Depends-Indep:
+# used by debian/rules.real to build linux-source
  patchutils <!stage1>,
+# used by upstream to build documentation
  xmlto <!stage1>,
 Vcs-Git: https://anonscm.debian.org/git/kernel/linux.git
 Vcs-Browser: https://anonscm.debian.org/cgit/kernel/linux.git